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BUREAt 

Main Classificati 

Sub-Classificatic ..^ , 

(Date when 01assifi( 

EXPLANATORY— Or Guide for Library Clerk. 

The "Book No." serves as an identification number; and not as a classification or 
a location number. [This number is given to each individual volume, making it sepa- 
rate and distinct, and said number is recorded in a regular " Accession Book."] 

"Main classification" corresponds to section or alcove; and "Sub-classification" 
to a subdivision of section or shelf. 

The "Book No." should be written in with ink, and the remaining lines should 
be filled in with pencil. The number never changes; the classification may, in certain 
cases, be changed. 







PRACTICAL TREATISE 



ON THE 



Combustion of Coal, 



INCLUDING 



DESCRIPTIONS OF VARIOUS MECHANICAL DEVICES FOR THE 

ECONOMIC GENERATION OF HEAT BY THE 

COMBUSTION OF FUEL, 



WHETHER 



SOLID, LIQUID OR GASEOUS. 



BY 

WILLIAM M. BARR. 



INDIANAPOLIS, IND.: 
YOHN BROTHERS 

1879. 



(VVwia, 



^ik 



COPYRIGHT. 

WILLIAM M. BAKR, 

1879. 
By transfer 

OCT 25 1915 



INDIANAPOLIS: 

BAKER & RANDOLPH, 

PRINTERS. 



y-uni 



PREFACE. 



This book is intended to present, within a moderate compass, 
the theory of the combustion of coal, with a view to adapting it to 
the needs of that large body of men to whom this subject is one of 
great interest, but who, on account of the abstruse style in which 
such books are generally written, can not easily obtain the desired 
information in regard to the chemistry of coal, its combustion, its 
calorific power, and other matters in this connection, which are not 
only of interest, but of importance to themselves. 

Perhaps no more lucid or accurate presentation of this subject 
has been written for engineers, than that embodied in Professor 
Rankine's "Steam Engine and Other Prime Movers," but that 
work, excellent as it is in itself, is to most persons a book by no 
means easy to read, or easy to use. It is not that this subject needs 
to be explained anew, or that there is anything to add to what has 
already been written, but it is rather to present to the non mathe- 
matical reader that which is accepted as high authority among 
engineers, in a language less difficult to understand. 

The absence then, of any purely practical treatise of recent 
date on this subject, and the belief that such a treatise would sup- 
ply a want has induced the preparation of this volume. The 
reader will judge for himself how far this want, if it ever existed, 
has been met. 

This book contains nothing that can be said to be new, but its 
usefulness need not be impaired on that account if it has the merit 
of presenting this subject in an accurate and intelligible manner. 
Much care has been bestowed upon the work to insure its accu- 
racy. The numerous instances in which the writer has converted 
French calories into British units of heat, in order to make quotations 
in the text of any practical value to the reader, has added not a 
little to the labor of preparation. Wherever quotations have been 
made from French, German or English writers using the metrical 
system, the measurements, quantities and temperature have been 
re-calculated and reduced to American equivalents and Fahren- 
heit degrees. 



IV PREFACE. 



In regard to authorities, Professor Rankin e's treatise, already 
referred to, has been consulted at almost every step wherever 
practicable and largely quoted from. Dr. Percy's treatise on 
"Fuel," has also been freely used and quoted from; so also, Watts' 
Dictionary of Chemistry; Ure's Dictionary of Arts, Manufacturers and 
Mines; The Geology of Pennsylvania, H. D. Rogers; the Geological 
Reports of the States of Ohio, Indiana and Illinois. 

Selections have also been made from well known and reliable 
contributors to the leading scientific journals, including the 
Engineer, Engineering, Scientific American, and others. The writer is 
also under many personal obligations, and especially so to Professor 
E. T. Cox, State Geologist, Indiana, not only for valuable contribu- 
tions of matter, which, from his thorough knowledge of coals, adds 
much to the value of the book, but for his personal interest and 
assistance in the preparation of the articles on the chemistry of 
coal. 

Perhaps an apology is needed for the space occupied by the 
re-print of the report of Dr. Gideon E. Moore on water-gas. To 
this I can only say, that it was furnished me at my own request, and 
inserted here on the conviction that a fuel-gas of some sort is one of 
the pressing needs of the day ; and as this report contains so much 
real information in regard to water-gas not only, but to gaseous 
fuel in general, I am sure it will amply repay a careful read- 
ing, for I believe our present imperfect methods of using crude 
fuels must, in the larger cities at least, give place sooner or later to 
the more economical employment of a fuel-gas. The exceeding 
low cost at which water-gas may be generated, its permanance, cer- 
tainty, ease of management, cleanliness and economy, are all, cer- 
tainly, in its favor. 

It will be observed there are repetitions here and there through 
the book ; these serve mainly as illustrations in the papers or lec- 
tures quoted from, so that it did not seem desirable to break the 
connection and re-write the sections containing them. 

Among the works consulted and quoted from, are the following, 
arranged in alphabetical order, and numbered. Wherever numbers, 
enclosed in brackets, occur throughout the text, they refer to the 
publications corresponding to the numbers as given below. 

Indianapolis, Ind., Maeoh 1879, 



Authors and Books Consulted or Quoted From. 



1. BRAMWELL, F.J. Science Lectures at South Kensington. Vol.1. London, 1878. 

Macmillan & Co. 

2. CLARK, D. K. Manual of Rules, Tables and Data, etc. London, 1877. Blakie & 

Son. 
:?. COOK, JOSIAH P. The New Chemistry. New York, 1871. D. Appleton & Co. 

4. COX, E. T. State Geologist, Indiana. Several volumes of reports quoted from, but 

the writer is also indebted for information contributed to this work by him 
from his laboratory record. 

5. CROOKS & ROHERIG. Metallurgy, Vol. 3— Fuel. London, 1870. Longmans, 

Green & Co. 

6. DAWSON, J. W. The Story of Earth and Man. New York, 1874. Harper & 

Bros. 
6%. DWIGHT, GEORGE S., in Scientific American, Feb. 24, 1877. 

7. ENCYCLOPEDIA BRITANNICA. IX Edition. 

8. ENGINEER. London. Several volumes quoted from. 

9. ENGINEERING. London. Several volumes quoted from. 

10. FARADAY, MICHAEL. Chemical History of a Candle. New York, 1861. Har- 

per it Brothers. 

11. FORNEY, M. N. Catechism of the Locomotive. New York, 1875. The Railroad 

Gazette. 

12. FOWNES, GEORGE. Elementary Chemist rg (Bridges). Philadelphia, 1871. Henry 

C. Lea. 

13. GRAHAM, THOMAS. Elements of Chemistry (Watts). New York, 1857. Charles 

E. Bailliere. 

14. MAXWELL, J. CLERK. Theory of Heat. New York, 1872. D. Appleton & Co. 

15. MAXWELL, J. CLERK. Lecture on Molecules. Bradford, September, 1873. 

Ifi. McCULLOCH, R. S. Mechanical Theory of Heat. New York, 1876. D. Van Nos- 
trand. 

17. MILLER, WILLIAM ALLEN. Elements of Chemistry. Part 1, Chemical Physics. 

New York, 1872. John Wiley & Son. 

18. McFARLANE, JAMES, in the Coal Trade Journal. 

19 NORTHCOTT, H. Steam Engine. London, 1877. Macmillan & Co. 

20. PERCY, JOHN. Metallurgy (Fuel). London, 1875. John Murray. 

21. PRESTON, S. TOLVER, in the Engineering (London). 

22. RANKINE, W. J. M. Steam Engine and other Prime Movers (Bamber). London, 

1876. Charles Gri$n & Co. 

23. ROGERS, H. D. Geology of Pennsylvania. Philadelphia, 1858. J. B. Lippin- 

cott & Co. 



VI AUTHORS AND BOOKS CONSULTED. 



24. SCIENTIFIC AMERICAN, New York. Several volumes quoted from. 

25. SCIENTIFIC AMERICAN, Supplement, New York. Several numbers quoted 

from. 

26. STEWART, BALFOUR. The Conservation of Energy. New York, 1874. D. 

Appleton & Co. 

27. STEWART, BALFOUR. Elementary Physics. London, 1873. Macmillan & Co. 

28. TAIT, P. G. Recent Advances in Physical Science. London, 1876. Macmillan 

& Co. 

29. TROWBRIDGE, WILLIAM P. Heat arid Heat Engines. New York, 1874. John 

Wiley & Son. 

30. TYNDALL, JOHN. Heat as a Mode of Motion. New York, 1874. D. Appleton 

&Co. 

81. TYNDALL, JOHN. Fragments of Science. New York, 1874. D. Appleton & Co. 

82. URE'S Dictionary of Arts, Mines and Manufactures. 

33. VOGEL, HERMANN. Chemistry of Light and Photography. New York. D. 

Appleton & Co. 

34. WATTS' Dictionary of Chemistry. 

35. WILLIAMS, C. WYE. Combustion of Coal (Weale's series). 



ERRATA. 

PAGE. LINE. CORRECTIONS (IN italics). 

16 third from top — but it also serves to show, etc. 

25 tenth from bottom — but, taken in connection with furnace combustion this pres- 
sure is of importance as a mechanical agency, etc. 



CONTENTS. 



CHAPTER I— Preliminary. page 
Physical Properties of Coal — Chemical Properties of Bodies — Divisibility of 
Matter — Molecules — Atoms — Atomic and Molecular Weights — Equivalent Num- 
bers—Symbolic Notation— Energy — Types of Energy — Conversion of Visible 
into Molecular Energy — Energy of Fuel — The Sun the Source of Energy — The 
Plants of the Coal Period— The Atmosphere of the Coal Period— The Influence 
of Light in the Formation of Coal — Dissipation of Energy 1 

CHAPTER II— The Atmosphere. 

Air the Source of Oxygen for Combustion — Composition of the Air — Nitrogen 
— The Chemical Compounds of Oxygen and Nitrogen — Properties of Oxygen — 
The Physical Properties of the Atmosphere — Absorption of Moisture — Cause of 
Rain — Radiation of Heat through the Air — Carbonic Acid and Ammonia in the 
Air — Ozone 25 

CHAPTER III— Fuels. 

Classification of Fuel — "Wood — Water Present in Wood— Composition of Wood 
— Wood Charcoal — Combustibility of Wood Charcoal — Peat — Analysis of Peat 
— Products of the Distillation of Peat — Peat as a Fuel— Peat Charcoal— Lignite 
—Difference between Lignite and Brown Coal — Lignite as a Fuel — Water in Lig- 
nite — Analysis of Lignites— Classification of Coal — Bituminous Coal — Analysis 
of Bituminous Coals— Non-caking Coals — Block Coal — Caking Coals — Gas Coal— 
Coke — The Influence of Temperature and Pressure in the yield of Coke — Cannel 
Coal — Semi-bituminous Coal — Semi-anthracite Coal— Anthracite Coal 35 

CHAPTER IV— Analysis of Coal. 

Analysis, Chemical, Qualitative, Quantitative, Proximate — Selection of Samples 
for Analysis — Method of Conducting a Proximate Analysis — Elementary Anal- 
ysis—Determination of Sulphur and Phosphorus — Carbon — Hydrogen — Carbur- 
eted Hydrogen — Sulphur — Products obtained from Coal 81 

CHAPTER V— Combustion. 

Chemical Attraction — Muriate of Zinc — Gunpowder — Physical Changes — Chem- 
ical Changes — Definite Proportions— Multiple Proportions — Carbonic Acid — 
Carbonic Oxide— Law of Equivalents— Energy of Chemical Separation — Nature 
of Combustion— Conditions Necessary to Combustion — Luminosity — Ignition — 
Flame — Recent Studies of Luminous Flames — Rate of Combustion — Tempera- 
ture of Fire — Weight and Specific Heat of the Products of Combustion — Avail- 
able Heat of Combustion— Efficiency of a Furnace 98 

CHAPTER VI — Air Required for Furnace Combustion. 

Proportions in which Oxygen unites with Carbon and Hydrogen — Air required 
for different Fuels — Heated Air for Combustion — Temperature of Air supplied 
to Blast Furnaces — The Hoffman Kiln — Berthier's Theory in regard to Heated 
Air — Peclet's Observations — Prideaux' Estimation of the value of Heated Air — 
Difficulties in Heating or Cooling Air — Proportions of Fire-Brick to Fuel burned 
in the Siemens Regenerative Furnace — Ponsard Furnace 126 

CHAPTER VII— The Furnace. 

Furnace Draft — Sectional Area of Chimneys — Height of Chimneys — Volume of 
Escaping Gases — Weight of Escaping Gases — Temperature of Escaping Gases — 
Distribution of Air in the Furnace— Admission of Air over the Fire — C. Wye. 
Williams' Plan — T. S. Prideaux' Plan— W. A. Martin's Plan — Experimental 
Test of the Martin-Ashcroft Furnace Door at U. S. Navy Yard, Washington — 
Perforated Pipes— Admission of Air at the Bridge-Wall — R. K. McMurray's Plan 
for admitting Heated Air— Admission of Air and Evaporation 136 

CHAPTER VIII— Products of Combustion. 

Carbonic Acid — Carbonic Oxide — Water — Nitrogen — Sulphurous Oxide — Sur- 
plus Air — Smoke — Products of Perfect Combustion Invisible — How Soot is 
Formed — Smoke-preventatives — The Corrosive Action of Sulphur on Boilers — 



tTlll CONTENTS. 



PAGE. 

Ashes and Clinker — Analysis of Coal Ashes — Color of Ashes as Indicating the 
Presence of Iron Pyrites in Coal — The Formation of Clinkers — The Influence of 
Iron in the Coal on the Formation of Clinker — Apparatus for Gas Analysis 158 

CHAPTER IX— Thermal Power of Fuels. 

Heat Developed by Chemical Action — Favre and Silberman's Apparatus — Units 
of Heat Evolved by Elemental Combustion — Heat Developed by the Combus- 
tion of Coal— Allotropic States of Carbon — Proximate Constitution of Coal — 
Experiments of Scheurer-Kestner and Meunier-Dollfus on the Calorific Power 
of Coal — Thompson's Calorimeter — Manner of Conducting Experiments — Evap- 
orative Power of Coal — Object in Reducing Evaporation to, from and at 212° 
Fahr 178 

CHAPTER X— Heat. 

Theory of Heat — Mechanical Force— Chemical Action — Relation of Atomic 
Weights to Specific Heat — Specific Heat of Simple Gases— Specific Heat and 
Atomic Weight of Elementary Substances — Specific Heat — Specific Heat of 
Water in its Three States — Specific Heat of Fuels — Specific Heat of Gases — 
Latent Heat — Latent Het of Fusion — Latent Heat of Evaporation — Mechanical 
Theory of Heat — Joule's Equivalent — Apparatus Emploved by Joule — Unit of 
Heat 195 

CHAPTER XI— The Construction op Furnaces. 

Construction Depends on the Fuel— Conditions attached to a Good Furnace — 
Why Ordinary Furnaces are so Wasteful — Volatilization of Gases in the Fur- 
nace — Quantity of Air Required — Force Blast — Description of a Reverberatory 
Furnace — Its Advantages — Increase of Efficiency bv the Use of Hot Air — Loss 
by Chimney Draft 208 

CHAPTER XII— Mechanical Firing. 

Objections to Hand Firing— Continuous Firing — The Requirements of a Self- 
feeding Mechanism— Description of M. Holroyd Smith's Furnace-Feeder 218 

CHAPTER XIII— Spontaneous Combustion of Coal. 

Most Likely to Occur on Board Ships — Vessels Lost from this Cause in 1874 — 
Spontaneous Combustion begins in the Center of the Heap or Middie of the 
Cargo — Iron Pyrites in Coal — How Carbon Spontaneously Ignites — Coal requires 
no Initial Temperature for its Combustion — No Limit to the Heat which may 
be produced by Concentration 223 

CHAPTER XIV— Coal-Dust Fuel. 

Continuous Firing — How a Furnace should be Fed when Using Powdered Fuel 
— Experiments of United States Government in 1S76 — Comparative Economy of 
Powdered Fuel as Compared with Ordinary Coal— Stevenson's Apparatus for 
Burning Coal-Dust 233 

CHAPTER XV— Liquid Fuel. 

Analysis of Crude Petroleum — Quantity of Air Required to Burn Oil — Units of 
Heat Evolved by the Combustion of Oil — Evaporative Power of Crude Oil — 
What is Claimed for Petroleum as a Fuel — Wise, Field and Aydon's System of 
Burning Liquid Fuel— Extraordinary Results Obtained— Advantages Arising 
from its Use on board Steamships and Vessels of War 245 

CHAPTER XVI— Gaseous Fuel. 

Loss Attending the Use of Solid Fuels — Advantages Connected with the Use of 
a Gas-Fuel — Coal-Gas for Domestic Use — Water-Gas — Volume of Water-Gas 
Obtained for One Ton of Coal Burned — Strong's Process for Generating Fuel- 
Gas — Professor Gruner Quoted on the Great Waste of Heat in Several Metallur- 
gical Processes — Comparison between the Efficiency of Crude Coal and Water- 
Gas — Calorific Intensity of Water-Gas — Analysis of Water-Gas — Calorific 
Equivalent of Water-Gas — Flame Temperature — Economic Value of Wa ter- 
ras— Influence of the Specific Heat of the Products of Combustion of Water- 
das — Water-Gas as an Illuminating Agent — Objections to Water-Gas 254 

CHAPTER XVII— Utilizing Waste Gases from the Furnace. 

Waste Products — Magnitude of the loss— Siemens' Regenerative Gas Furnace.... 284 

CHAPTER XVIII— A. Ponsard's Process and Apparatus for Generating 
Gaseous Fuel 290 



CHAPTER I. 

PRELIMINARY. 

Physical Properties of Coal — Chemical Properties of Bodies— Divisi- 
bility of Matter — Molecules — Atoms — Atomic and Molecular 
Weights — Equivalent Numbers — Symbolic Notation — Energy — ' 
Types of Energy — Conversion of Visible into Molecular Energy 
— Energy of Fuel — The Sun the Source of Energy — The Plants 
of the Coal Period — The Atmosphere of the Coal Period — The 
Influence of Light in the Formation of Coal— Dissipation of 
Energy. 

The Physical Properties of Coal include most of the 
general properties of matter. It belongs to the non- 
metallic class of bodies, is a solid, varying in structure 
from hard crystalline, as in the case of pure anthracite, 
through all gradations to a compact earthy body bear- 
ing a close resemblance to wood, both in structure and 
appearance, and presenting no distinct crystalline frac- 
ture when broken. In color it varies from black to 
dark brown. It is always brittle, and may easily be 
broken into fragments. Anthracites do not fuse at all 
in the lire ; bituminous coals sometimes fuse, but not 
without decomposition. In specific gravity it varies 
from 1.55 to 1.20. 

Coal occurs in strata of varying thickness and purity. 
Carbon and hydrogen are its chief elements, and are 
those which allow its use with advantage as a source of 
heat. 

(2) 



COMBUSTION OF COAL. 



The Chemical Properties of a Body are those which 
relate to its action upon other bodies, and to the perma- 
nent changes which it experiences in itself, or which it 
effects upon them. When a bod}^ undergoes chemical 
change it almost invariably destroys the physical prop- 
erties held by it previous to this change, but experiment 
has fully demonstrated that matter is indestructible, so 
that whatever changes are made in the physical appear- 
ance or form of matter by any chemical process, none 
of it is destroyed. 

Divisibility of Matter — A piece of coal may be divided 
and subdivided until it is reduced to an impalpable pow- 
der and still retain all the characteristics of coal, and 
we might keep on dividing a single grain of this coal — 
if our senses were acute enough to detect, and we had 
instruments sufficiently delicate to perform the subdivis- 
ions — until at last there would be a piece no longer cap- 
able of being subdivided without destroying its com- 
position or nature, there would then be, as a final result, 
a molecule of coal. If we were to analyze this molecule 
of coal we would find it to be composed of several sub- 
stances, such as carbon, hydrogen, oxygen, nitrogen, 
etc., so that taking a molecule of coal we may reduce it 
to the elementary substances, which gave it character. 
These elementary substances are capable of farther 
subdivision in the same manner, and if any molecule 
were separately subdivided until it was no longer pos- 
sible to divide it again, such a piece would be called an 
atom — not of coal, but of carbon, hydrogen, oxygen, or 
whatever else it might be. This process would be 



MOLECULES. 



partly mechanical and partly chemical. The crashing 
or reducing to powder would be mechanical; the resolv- 
ing of the coal into its elements by decomposition is a 
chemical process. Any compound substance may be 
resolved into its constituent molecules, and these into 
atoms, which is the ultimate limit of the divisibility of 
matter. 

Molecules (15) — An atom is a body which can not he 
cut in two. A molecule is the smallest possible portion 
of a particular substance. Any substance, simple or 
compound, has its own molecule. If this molecule he 
divided, its parts are molecules of a different substance 
or substances from that of which the whole is a molec- 
ule. An atom, if there is such a thing, must be a molec- 
ule of an elementary substance. 

The old atomic theory, as described by Lucretius and 
revived in modern times, asserts that the molecules of 
all bodies are in motion, even when the body itself 
appears to be at rest. These motions of molecules are, 
in the case of solid bodies, confined within so narrow 
a range that even with our best microscopes we can not 
detect that they alter their places at all. 

In liquids and gases, however, the molecules are not 
confined within any definite limits, but work their way 
through the whole mass, even when that mass is not dis- 
turbed by any visible motion. This process of diffusion, 
as it is called, which goes on in gases and liquids and 
even in some solids, can be subjected to experiment and 
forms one of the most convincing proofs of the motion 
of molecules. Now, the recent progress of molecular 



COMBUSTION OF COAL. 



science began with the study of the mechanical effect of 
the impact of these moving molecules when they strike 
against any solid body. Of course these flying molec- 
ules must beat against whatever is placed among them, 
and the constant succession of these strokes is, accord- 
ing to our theory, the sole cause of what is called the 
pressure of air and other gasses. 

"We all know that air or any other gas placed in a 
vessel presses against the sides of the vessel, and against 
the surface of any body placed within it. On the kin- 
etic theory this pressure is entirely due to the molecules 
striking against these surfaces, and thereby communi- 
cating to them a series of impulses, which follow each 
other in such rapid succession that they produce an 
effect which can not be distinguished from that of a 
continuous pressure. If the velocity of the molecules 
is given, and the number varied, then since each molec- 
ule on an average strikes the side of the vessel the 
same number of times, and with an impulse of the same 
magnitude, each will contribute an equal share to the 
whole pressure. 

The pressure in a vessel of a given size is, therefore, 
proportional to the number of molecules in it, that is 
to the quantity of gas in it. 

This is the complete dynamical explanation of the 
fact discovered by Robert Boyle, that the pressure of air 
is proportioned to its density. It shows also that of dif- 
ferent portions of gas forced into a vessel, each produces 
its own part of the pressure independent of the rest, and 
this whether these portions be of the same gas or not. 



ATOMIC AND MOLECULAR WEIGHTS. 



Atomic and Molecular Weights — "Equivalent num- 
bers " are often used to express either atomic or molec- 
ular weights, and not unfrequently both. Confusion 
arises in not stating in precise terms which of the two 
is meant. By referring to one book we find, 11 = 1, C 
= G, = 8 and S = 16, etc. By referring to another book 
we find, H=l, C = 12, = 16 aiuh S = 32, etc. The law 
of definite proportion assumes that atoms have definite 
weight; that an atom is a definite and fixed quantity; 
that atoms of the same substance are of the same size 
and weight. The confusion arises not that matter has 
changed, or that the law of proportion Ifas changed, but 
the nomenclature of the new r chemistry is different from 
the old in the introduction of the word molecule as a 
substitute for the w r ord atom as it was generally used, 
and though still retaining it, gives it a specific mean- 
ing w T hich is not synonymous or equivalent to the word 
molecule. 

This word molecule means simply a small mass of 
matter or the smallest portion of a particular substance; 
an atom means indivisible. 

Hydrogen being the lightest knowui substance, has, 
by general consent, been made the unit of comparison. 
It is to be supposed, to begin with, that a molecule of 
hydrogen consists of two atoms ; hence, if the atomic 
weight of hydrogen is to be taken as 1, the molecular 
weight is 2. (7). In order to ascertain the molecular 
weights of other substances — that is to say, the relative 
weights of their molecules referred to that of hydrogen 
— it is merely necessary to determine their densities 



6 



COMBUSTION OF COAL. 



referred to hydrogen as unity, and then multiply their 
densities by 2. 

"When, however, the molecular weights of the ele- 
ments are compared with their atomic weights it is 
found they do not always, as in the case of hydrogen, 
double their atomic weights ; hence it is inferred that 
the molecules of elements do not all contain two atoms. 
In a few cases the atomic weights and the molecular 
weights agree, which necessitates the conclusion that 
the molecules are monatomic or consist of a single atom; 
in a few other cases the molecular weight is either four 
or six times the atomic weight, and the molecules are 
therefore regarded as tetratomic or hexatomie ; that is, 
containing four or six atoms. 

The following table gives the molecular weight of 
the constituents of coal as ordinarily determined by 
analysis, adding phosphorus which occurs occasionally, 
but inore particularly, to exhibit its molecular as com- 
pared with the atomic weight, illustrating what was said 
in the preceding paragraph : 

Table I — Molecular Weights. 



SYMBOL. 


ATOMIC 


MOLECULAR 


WEIGHT. 


WEIGHT. 


H 


1 


2 


C 


12 


24 


N 


14 


28 





16 


32 


P 


31 


124 


s 


32 


f 04 
1 192 



NUMBER OF 

ATOMS IN 
A MOLECULE. 



Hydrogen... 

Carbon 

Nitrogen 

Oxygen 

Phosphorus 
Sulphur 



ATOMIC AND MOLECULAR WEIGHTS. 



It will be seen that two numbers are given for sul- 
phur. This is because at temperatures above 800° C. 
(1472° Fahr.) the density of sulphur vapor is such as to 
indicate that the sulphur molecule consists of tw r o atoms, 
whereas its density at about 500° C. (932° Fahr.) is three 
times as great, and, consequently, it is said to be sup- 
posed that the molecules are hexatomic or contain six 
atoms. 

Table II contains a list of elements found in coal by 
elementary analysis. 

Table II. 



NAME 

Aluminum 

Calcium 

Carbon 

Hydrogen 

Iron 

Magnesium 

Nitrogen , 

Oxygen 

Phosphorus.,. 

Potassium 

Silicon... 

Sulphur 



ATOMIC 
W EIGHT. 



27.5 

40. 
12 
1 
56 
24 
14 
16 
31 
39 
28 
32 



The column of atomic weights in this table means 
that one atom of carbon is twelve times as heavy as 
hydrogen, oxygen sixteen times as heavy, nitrogen four- 
teen times as heavy, etc. 



COMBUSTION OF COAL. 



A distinction must be made between atomic weights 
and equivalent numbers. They do not mean the same 
thing. The equivalent or combining proportion is 
an experimental constant which is independent of the- 
oretical considerations; (17) but the relative atomic 
weight is necessarily a matter of inference, and may be 
a number, often a multiple of the equivalent, and 
selected by the chemist from theoretical considerations, 
based partly upon the law of gaseous volumes, partly 
on chemical grounds, partly on the phenomena of spe- 
cific heat. 

The law of gaseous volumes, as laid down by Avo- 
gadro, means that equal volumes of all gasses under the 
same conditions have the same number of molecules (3). 
Then, since a given volume of oxygen gas weighs six- 
teen times as much as the same volume of hydrogen gas 
the molecule of oxygen must weigh sixteen times as 
much as the molecule of hydrogen ; and, if we assumed 
the hydrogen molecule as the unit of molecular weight, 
the molecule of oxygen would weigh sixteen of these 
units, hence the atomic weight of oxygen would be six- 
teen. 

Symbolic Notation — In the preceding tables, the let- 
ters II for hydrogen, C for carbon, etc., appear; this is 
for two reasons : 

1. It belongs to an agreed symbolic language by 
which elements may be recognized at sight by the use 
of the first letter, as far as practicable, of its Latin 
name. 



SYMBOLIC NOTATION. 9 



2. It facilitates the representation of chemical 
changes, by which reactions of a complicated character 
may be understood at a glance. 

These symbols are not simply abbreviations of the 
names of the elements, but represent the atomic weights 
of the elements for which they stand; thus, C repre- 
sents carbon not only, but its atomic weight as well, 
and may be expressed as follows: Carbon = C= 12. 
This is not an exact expression, but serves to show the 
value of C as a symbol, representing the name of the 
element carbon, and its atomic weight, 12. Whenever 
a symbol is used singly, it means an atom of the 
element represented ; C represents carbon not only, but 
one atom of carbon. A combination of elements is 
represented by a combination of symbols placed side by 
side; thus — one atom of carbon and one atom of 
oxygen would be expressed as CO, and by this we 
mean carbonic oxide, a very common product of the 
combustion of coal. 

We also understand by this, that one atom of carbon 
and one atom of oxygen combine to form, not one atom, 
but one molecule, of carbonic oxide. 

Suppose we added to the molecule of carbonic oxide 
(CO), another atom of oxygen, or CO 4- 0, we under- 
stand the compound to consist of one atom of carbon 
and two atoms of oxygen, and, as a less complicated 
expression the formula C0 2 is used. This is the sym- 
bolic expression of one molecule of carbonic acid, the 
product of the complete combustion of carbon and 
oxygen. The atomic value of each element in a com- 



10 



COMBUSTION OF COAL. 



pound remains unchanged, and the aggregate weight of 
the atoms forms the molecular weight of the compound, 
whatever it may he. 

One molecule of carbonic acid = one atom carbon C X 12 = 12 

two atoms of oxygen 2 X 16 = 32 



C0 2 =44 
the weight of one molecule of carbonic acid. 

Whenever two or more atoms of a hody enter into 
the formation of a molecule, it is most conveniently 
expressed hy writing a small figure to the right of the 
letter and helow the line, whenever practicable, or 
making it smaller than the symbol, when not so; 
C 3 indicates three atoms of carbon, H 8 = 8 atoms of 
hydrogen ; C 3 H 8 is the formula for one of the products 
of coal occurring in the Marsh gas series, and known 
as prophyl hydride, and this formula is the expression 
of one molecule. 2 C 3 H 8 would be the expression repre- 
senting two molecules, and so on. 

Secondary compounds, such as salts, are expressed 
in an analogous way, the metal being usually placed 
first, Ca C0 3 representing one molecule of carbonate of 
calcium — calcium being the metallic base (17). 

When a comma is used to separate two compounds, 
a more intimate union is supposed than when the sign 
+ is used. 

Suppose in the analysis of the product of the com- 
bustion of coal we have in 100 parts the formula 87 
C0 2 -f 13 II 2 as representing the constituents of the 
sample analyzed. It means that 87 per cent, is carbonic 



TYPES OF ENERGY. 11 



acid, and 13 per cent, water or vapor, as the latter will 
probably be condensed and disappear, while the former 
may still retain its permanancy as a gas; the sign -f- is 
interposed to separate or distinguish the one from the 
other. 

A very little practice will enable one to determine 
at sight the elements in any formulated compound, and 
give to each its proper atomic weight. 

Energy is the power of doing work. By work is 
meant overcoming resistance. If a body weighing one 
pound be lifted one foot high against the action of 
gravity, we have then the unit of work called a foot- 
pound. Thirty-three thousand pounds raised one foot 
high in a minute is called a horse-power. Five hun- 
dred and fifty pounds raised one foot high in a second 
amounts to the same thing, because : 550 lbs. X 60 
sec. == 33,000 lbs. one foot high in 60 seconds or 1 minute. 

The unit of work as laid down in most foreign sci- 
entific books is the kilogrammetre ; this represents the 
work done in raising one kilogramme one metre high 
against the force of gravity at the earth's surface. This 
unit of work is rarely used in this country, and, unless 
otherwise stated when used, we shall employ the foot- 
pound as the unit of work in this book. 

Types of Energy — Energy is of two types, known as 
kinetic and potential. 

Kinetic energy is the energy due to motion. 
Potential energy is the energy due to position. 



12 COMBUSTION OF COAL. 

Let us suppose a brick house in course of erection, 
and attained a height of, say, twenty feet above the 
ground; a man standing on the ground may throw a 
brick to another man on the scaffold, at that height. If, 
instead of using his muscular strength to throw the 
brick to that height, he simply a let go" of the brick, it 
would, in obedience to the law of gravitation, fall to the 
ground; but, instead, he gives the brick a toss, and it 
ascends against the attraction of the earth to something 
more than the height of the scaffold, ceases to rise, and 
begins to fall when the man above catches it, and places 
it beside him on the scaffold. "We have in this simple 
illustration examples of the two types of energy. The 
flight of the brick upwards is due to the impulse it 
received at the hands of the man on the ground — it is a 
consequence of muscular effort — it is an example of 
work done, because, resistance has been overcome. The 
brick in its flight has a property which it did not have 
on the ground. That property is energy — energy due 
to motion, or kinetic energy. The amount of energy or 
capacity it has for doing work is a certain quantity, and 
is equal to the weight of the brick multiplied into the 
height it ascended above the man's hands before it began 
its downward flight. 

The brick on the scaffold is at a state of rest, but it 
has not lost its energy. It is, however, of a different 
type from that in the preceding paragraph. The brick 
on the scaffold, though at rest, has a capacity for doing- 
work simply on account of its elevation. 



VISIBLE INTO MOLECULAR OR INVISIBLE ENERGY. 13 

This is called the energy of position or potential 
energy. Suppose the brick to be pushed over the edge 
of the scaffold ; it will fall by virtue of gravitation, and 
when it reaches the height of the man's hands, from 
which the brick was projected upward, the two energies 
will exactly equal each other, except in so far as it is 
modified by the resistance of the air. This, however, 
gives no exception to the general truth of the principle 
of conservation of energy, because any energy lost by 
the brick is communicated without loss of quantity to 
the surrounding air. 

These two kinds of energy, energy of motion and 
energy of position, are being continually changed one 
into the other. An illustration of this conversion of 
one form of energy to another is seen in a head of water 
employed to turn a water wheel. The water in the dam 
possesses energy on account of its height above the 
wheel. The weight of this water impinging against the 
arms of the wheel imparts motion to it, and, we have 
in the wheel a store of energy due to motion, which, by 
suitable connections, is capable of doing work. This is 
an example of the transmutation of energy; that is, the 
changing of one kind of energy into another. There 
are many varieties of visible energy, but there is energy 
which is invisible, and, the one may be converted into 
the other. The most common illustration of this is the 
conversion of work into heat. 

Conversion of Visible into Molecular or Invisible Energy 
— This occurs when motion is arrested, whether by per- 
cussion or by friction. It is the conversion of work into 



14 COMBUSTION OF COAL. 

heat. If a lead bullet be fired against an iron target its 
motion is destroyed by impact, but not so its energy. 
The ball will have performed work in the act of flatten- 
ing itself, and in rebounding from the target, but in 
addition to this it will be found to be quite hot. If we 
had an instrument delicate enough to measure the tem- 
perature of the target after the ball had come in contact 
with it, we would find it to be higher than it was before 
the ball struck it. If we could gather together the 
friction of the ball in the gun, the resistance of the ball 
in the air, the work done in overcoming gravitation, the 
work done in the act of flattening the ball, the work 
done in the rebound, the work done in producing the 
tremor of the target, together with the heat generated 
by impact, we would then have an amount of energy 
exactly equal to the energy imparted to the ball by the 
powder at the moment of explosion. A conversion of 
visible or actual energy into heat. 

If two pieces of dry wood are rubbed together with 
considerable pressure they get quite hot, and it is possi- 
ble, if this rubbing were continued long enough, they 
would in time "take fire" and burn. The ordinary 
explanation of this is, that heat has been generated by 
friction. This is quite true, but it is also to be explained 
on the theory that work has been converted into heat. 

The great characteristic of energy is, that it may be 
transformed or transmuted from one kind of energy into 
another kind of energy, but through all its transforma- 
tions the quantity present always remains the same; 
though known by different names, we ought not to for- 



ENERGY OF FUEL. 



get that energy is always the same thing, and the various 
names given to energy are simply those of convenience 
in classification. 

Energy of Fuel — The principal fuel in all civilized 
countries is coal. It contains, within an unattractive 
exterior, a store of energy almost incredible. Having 
an area in this country alone, of nearly two hundred 
thousand square miles of coal formation, we may form 
some idea of this vast force now latent, hut ready to obey 
the law of its nature, demanding only that the conditions 
be favorable for the conversion of its constituent elements, 
through the agency of a chemical union with oxygen, 
in order to convert this passive and inert mass of car- 
bonaceous matter into heat, a force, capable of per- 
forming greater or less work through the medium of 
heat engines, as the conditions are more or less favora- 
ble for economic conversion. 

The greater part of the coal formation in this coun- 
try is bituminous ; it contains less carbon than anthra- 
cite, but its heating power, pound for pound, is not 
much less if pure, and free from earthy matter. The 
volatile portions being rich in hydro-carbon, giving off 
great heat if combustion is perfect. 

The energy of fuel or its power to do work may 
easily be computed by assuming a value of 14,500 heat 
units in one pound of coal, this multiplied by 772, the 
thermal unit known as Joule's equivalent would give : 
14,500X772 = 11,194,000 pounds raised one foot high in 
one minute, representing the potential energy of one 
pound of coal. 



16 COMBUSTION OF COAL. 

This of course represents the utmost limit of work 
in one pound of coal, and which never can be arrived at 
in practice, but it also seems to show the vast store of 
energy in the coal, and the latent, force capable of min- 
istering to our needs, by the simplest mechanism. 

The Sun the Source of Energy — If we would know 
the beginnings of coal formation we must go back 
through the ages to the period known as the carbon- 
iferous age. Coal is believed to be vegetable matter, 
which has undergone both chemical and mechanical 
changes during the ages in which it has been buried 
under the strata of the earth's crust. The flora of that 
period was rank in the extreme; fortunately, specimens 
occur by which a "restoration" of the characteristic 
plants which play so important a part in coal formation 
having been carefully removed, and serve to show not 
only the structure of the plant, interesting in itself, but 
gives us an idea from our knowledge of tropical vegeta- 
tion how intense the heat, and how humid the atmos- 
phere, laden with carbonic acid, stimulating all vegeta- 
tion to collossal growth. 

Wood exposed to the oxygen of the atmosphere is 
slowly but entirely rotted and destroyed; even if buried, 
the oxygen having access through the particles of sand 
will in time produce the same result ; but if the action 
of the oxygen of the atmosphere is nearly or entirely 
prevented, the woody matter is slowly burned into coal. 
This proceeding does not come to its end without a 
great many changes. One of these modifications is the 
transformation of the woody matter into a soft black 



THE SUN THE SOURCE OF ENERGY. IT 

mud; the ever-increasing strata above this formation 
varying from hundreds to thousands of feet crushes 
together the cell walls of the vegetable matter, pro- 
ducing not only a flattening but a hardening effect by 
reason of this immense pressure, the intensity of which 
may be imagined if we suppose earth, rock, etc. to 
weigh about eighty pounds per cubic foot on an average. 

The most conspicuous and abundant of the trees of 
the coal period was the sigillaria or seal tree. They grew 
to a height from thirty to sixty feet, though they are 
said to have attained a height of seventy feet and 
a diameter of five feet. They, more than any 
other genus of plants, contributed to the coal forma- 
tion. Some twenty-eight varieties of this tree are 
described in the Geology of Pennsylvania— Rogers — 
vol. ii, p. 871-3. 

" These trees (6) present tall, pillar-like trunks, 
and marked by rows of scars left by the fallen leaves. 
They are sometimes branchless, or divide at the top 
into a few thick limbs, covered with long, rigid 
grass-like foliage. On their branches they bear long, 
slender spikes of fruit, and we may conjecture that 
quantities of nut-like seeds scattered over the ground 
around their trunks are their produce. If we approach 
one of these trees closely, more especially a young spec- 
imen not yet furrowed by age, we are amazed to observe 
the accurate regularity and curious forms of the leaf- 
scars, and the regular ribbing so very different from that of 
our ordinary forest trees. If we cut into its stem, we are 
still further astonished at its singular structure. Exter- 
(3) 



18 COMBUSTION OF COAL. 

nail j it has a firm and hard rind; within this is a great 
thickness of soft cellular inner Lark, traversed by large 
bundles of tough fibres. In the center is a core or axis 
of woody matter, very slender in proportion to the thick- 
ness of the trunk, and still further reduced in strength 
by a large cellular pith. Thus a great stem four or five 
feet in diameter is little else than a mas3 of cellular tis- 
sue, altogether unfit to form a mast or beam, but excel- 
lently adapted, when flattened and carbonized, to blaze 
upon our winter hearth as a flake of coal. The roots of 
these trees were perhaps more singular than their stems; 
spreading widely in the soft soil by regular bifurcation, 
they ran out in long, snake-like cords, studded all over 
with thick C3dindrical rootlets, which spread from them 
in every direction. They resembled in form, and proba- 
bly in function, those cable like root-stocks of the pond- 
lilies, which run through the slime of lakes, but the struct- 
ure of the rootlets was precisely that of those of some 
modern Cycads. It was long before these singular roots 
were known to belong to a tree. They were supposed 
to be branches of some creeping aquatic plant, and bot- 
anists objected to the idea of their being roots; but at 
length their connection with sigillaria was observed sim- 
ultaneously by Mr. Binney, in Lancashire, and by Mr. 
Richard Brown, in Cape Breton, and it has been con- 
firmed by many subsequently observed facts. This con- 
nexion, when once established, further explained the 
m of the almost universal occurrence of Btigmaria, 
ai hese roots were called, under the coal beds; while 
i ks of the same plants were the most abundant fossils 



THE SUN THE SOURCE OF ENERGY. 19 

of their partings and roofs. The growth of successive 
generations of sigillaria was, in fact, found to he the 
principal cause of the accumulation of a hed of coal. 1 ' 

We have not the space to devote to the numerous 
other plants found in coal formation, nor to the success- 
ive cosmieal changes which for ages have buried these 
plants so far beneath the present surface of the earth, 
but wish to show that the sun which gave to these 
plants both light and heat is really the source from 
whence all this energy is derived. 

Prof. Tyndall, in his "Heat as a mode of motion" 
quotes (section 707) from Sir John Hershel,* "The 
sun's rays are the ultimate source of almost every 
motion which takes place on the surface of the earth. 
By its heat are produced all winds, and those distur- 
bances in the electric equilibrium of the atmosphere 
which give rise to the phenomena of lightning, and 
probably also to terrestrial magnetism and the aurora. 
By their vivifying action, vegetables are enabled to 
draw support from inorganic matter, and become in 
their turn the support of animals and man, and the 
source of those great deposits of dynamical efficiency 
which are laid up for human use in our coal-strata. 
By them the waters of the sea are made to circulate in 
vapor through the air, and irrigate the land, producing 
springs and rivers. By them are produced all distur- 
bances of the chemical equilibrium of the elements of 
nature, which, by a series of compositions and decom- 
positions, give rise to new products and originate a 
transfer of materials. Even the slow gradation of the 

* Outlines of Astronomy, 1833. 



20 COMBUSTION OF COAL. 

solid constituents of the surface, in which its chief 
geological change consists, is almost entirely due, on the 
one hand, to the abrasion of wind or rain and the 
alternation of heat and frost ; on the other, to the con- 
tinual beating of sea- waves agitated by winds, the 
results of solar radiation." 

In section 710 Prof. Tyndall says: "In the building 
of plants, carbonic acid is the material from which the 
carbon of the plants is derived, while water is the sub- 
stance from which it obtains its hydrogen. The solar 
beam winds up the weight; it is the agent which severs 
the atoms, setting the oxygen free, and allowing the 
carbon and the hydrogen to aggregate in woody fibre. 

If the sun's rays fall upon a surface of sand, the sand 
is heated, and finally radiates away as much heat as it 
receives; but let the same beams fall upon a forest; 
then the quantity of heat given back is less than that 
received, for a portion of the sun-beams is invested 
in the building of the trees. Without the sun, the 
reduction of the carbonic acid and water can not be 
effected, and, in this act, an amount of solar energy is 
consumed exactly equivalent to the molecular work 
done." 

Dr. Hermann Vogel, in his treatise on " The chem- 
istry of light and photography,"* shows the chemical 
effect of sun-light on plants, and especially the modified 
growth of plants owing to differences in the intensity 
of light. He says, " These variations in the chemical 
intensity of light arc very important to the life of 
plants. The green leaves of plants inhale carbonic acid 

*D. Applcton & Co., N. Y., 1875. 



THE SUN THE SOURCE OF ENERGY. 21 

and exhale oxygen under the influence of light. But 
this breathing process does not take place without the 
presence of light. The green color of leaves and the 
variegated scale of colors in flowers exist only under 
the operation of light. In the dark, plants only develop 
sickly blossoms, like the well known white germs of 
potatoes kept in cellars. 

" The necessity of light for the life of plants is also 
seen in the effort made by plants kept in darkened rooms 
to reach the apertures which admit light, growing, as it 
were, toward them. Hence a plant developes with an 
energy proportioned to the intensity of the light. 
Accordingly, the greater fruitfulness of the tropics is to 
be ascribed, not only to the higher temperature, but also 
to the greater chemical intensity of the light. Recent 
observations have established that the yellow and red 
rays, and not the blue and violet, produce the greatest 
chemical effect on the leaves of plants. 

"We have now arrived at the knowledge of the 
importance of light for the economy of nature. 

" There was a time when the atmosphere was richer 
in carbonic acid gas than now. When the incandescent 
and fluid masses that once formed our earth gradually 
became condensed, when the watery vapors were precip- 
itated as seas, the atmosphere contained almost all the 
carbon of the earth after combustion; that is, united 
with oxygen as carbonic acid gas. The air was, there- 
fore, at that time infinitely richer in carbonic acid than 
now. When at length the earth had cooled sufficiently 
for vegetation to be developed, gigantic plants shot forth 



22 COMBUSTION OF COAL. 

from the warm ground under the influence of the sun- 
light. They flourished luxuriantly in the atmosphere, 
rich in carbonic acid, the carbon of the carbonic acid 
passed over into the form of wood, and thus in the course 
of thousands of years it was continuously diminished. 
Revolutions of the earth's surface succeeded ; whole ter- 
ritories, with their forests, were buried under sand and 
clay beds, and, becoming decomposed, were changed 
into coal. A fresh vegetation sprouted forth from the 
newly formed soil, and again absorbed, under the influ- 
ence of light, the carbonic acid of the atmosphere, to be 
once more engulfed by a fresh cataclysm. Thus the car- 
bonic acid of the atmosphere was stored as coal in the 
depths of the earth ; and thus the atmosphere, by the 
chemical effects of light, became continually richer in 
oxygen, until at length, after countless revolutions of the 
earth, it obtained that wealth, oxygen, which made the 
existence of man possible, where he appeared at the 
end of the earth's development. 

"We see, therefore, that the chemical influence of 
light has played an important part in the development 
of our planet, and it continues to do so in the economy 
of nature." 

Dissipation of Energy — If we attempt to cany out in 
practice the theory that any form of energy may be 
transferred into another form without loss of useful 
effect, we shall be sadly disappointed. This has been 
the fruitless field so long cultivated by the seekers after 
a perpetual motion. The mistake has been made by 
them in this — in supposing that the various forms of 



DISSIPATION OF ENERGY. 23 

energy may be transformed into mechanical energy or 
made to do work without the loss incident to the absorp- 
tion by the various other forms of energy which are 
contiguous, and which are constantly seeking fresh sup- 
plies of energy from a source higher than their own. 
If these processes were not only transformable but 
reversible, then perpetual motion would be a fact. 

We know that heat, as a form of visible mechanical 
energy, is available only as we use it from a higher to a 
lower temperature, and we know further, that, once the 
heat has spent its energy or capacity for doing work, 
there is no way by which it can be restored. Heat may 
be made to do work, and work may be transferred into 
heat, but the processes are not reversible. 

This does not in the least invalidate what is known 
as the mechanical equivalent of heat, for it takes into 
account all the losses incident to the transfer of availa- 
ble energy, but the transfer once made, complete restor- 
ation is impossible. 

In all cases there is a tendency for the useful energy, 
whenever a transformation takes place, (28) to run down 
in the scale — that, the quantity being unaltered, the 
quality becomes deteriorated, or the availability becomes 
less; and from similar results in all branches of physics 
we are entitled to enunciate, as Sir William Thompson 
did very early after the new ideas were brought into 
full development, the principle of dissipation of energy 
in nature. 

The principle of dissipation, or degradation, as I 
should prefer to call it, is simply this, that as any opera- 



24 COMBUSTION OF COAL. 

tion going on in nature involves a transformation of 
energy, and every transformation involves a certain 
amount of degradation (degraded energy meaning 
energy less capable of being transformed than before), 
energy is continually becoming less and less trans- 
formable. 

As long as these changes are going on in nature, the 
energy of the universe is getting lower and lower in the 
scale, and you can see at once what its ultimate form 
must be, so far, at all events, as our knowledge yet 
extends. Its ultimate form must be that of heat so 
diffused as to give all bodies the same temperature. 
Whether it be a high temperature or a low temperature 
does not matter, because whenever heat is so diffused as 
to produce uniformity of temperature, it is in a condi- 
tion from which it can not raise itself again. In order 
to get any work out of heat, it is absolutely necessary 
to have a hotter body and a colder one; but if all the 
energy in the universe be transformed into heat, and if 
it be in all bodies at the same temperature, then it is 
impossible — at all events by any process we know of as 
yet — to raise the smallest part of that energy into a 
more available form. 



CHAPTER II. 

THE ATMOSPHERE. 

Air the Source of Oxygen for Combustion — Composition of the 
Air — Nitrogen — The Chemical Compounds of Oxygen and 
Nitrogen — Properties of Oxygen — The Physical Properties of 
the Atmosphere — Absorption of Moisture — Cause of Rain — 
Radiation of Heat through the Air — Carbonic Acid and 
Ammonia in the Air — Ozone. 

Atmospheric Air — The source of oxygen, as a sup- 
porter of furnace combustion, is atmospheric air. The 
exact composition of the atmosphere has been made the 
subject of experimental research, and from samples 
taken at different heights. above the level of the sea, as 
well as depths below it; from nearly every quarter of 
the globe ; analysis show it to be essentially the same. 
The height of the atmosphere has not been accurately 
determined, but it is supposed to be about forty-live 
miles. The pressure of the atmosphere is one of its 
most important properties, not only in the ordinary 
economy of nature, but as a mechanical agency in pro- 
ducing draught in the furnace. The measured quantity 
of this pressure is found to be equal to a column of 
mercury having one square inch of area by thirty inches 
in height, or, taking the weight of the mercury instead, 
we then have 14.73 lb. as the weight of the atmosphere ; 
subject, however, to changes of temperature, humidity, 
etc. In all ordinary calculations it is assumed that 32 
feet of water, 30 inches of mercury or 15 lbs. equal- the 
pressure of the atmosphere. 



26 COMBUSTION OF COAL. 

Air was long believed to be simple substance, and 
when its composite nature was discovered, and it was 
found to be a combination of nitrogen and oxygen, the 
first supposition was that the union was a chemical one, 
but farther research showed the mixture to be mechan- 
ical. We have already stated that when two bodies 
unite with each other chemically, the product of this 
combination is a compound differing from the elements 
of which it is composed. The union of these two gases 
in the proportions approximating four volumes of nitro- 
gen to one of oxygen gives common air, and this union 
is distinguished by no properties which may not be 
attributed individually to these gases. 

From this circumstance, not alone, but from the fact 
that every experiment to determine whether this union is 
a chemical one, there has been so far no indication that 
the union is other than mechanical. 

The composition of atmospheric air varies in differ- 
ent localities, owing to local causes, but these changes 
are so minute that it is extremely difficult to detect com- 
bining gases. A mean composition of atmospheric air 
shows it tcpbe composed of, 

I VOLUME. W & 

V pkk cknt. ^«r#e»ifc-, 

ISfitr^gen 79 /*J 

Oxygen 21 Z 3 

ioo 7*i? 

Aqueous vapor is present in the air at all times, even 
at the lowest temperatures yet observed. 

From three to ten volumes of carbonic acid in ten 
thousand parts of air have also been observed. 



NITROGEN. 27 



The weight of one cubic foot of air at 32° Fahr. is 
.030723 ib. or 565.1 grains ; at 62° it is .076097:tb. or 532.7 
grains. The volume of one pound of air at 32° Fahr. 
at ordinary atmospheric pressure (14.7 lbs.) is 12.4 cubic 
feet. 

Nitrogen — By volume and by weight nitrogen is the 
principal constituent of the atmosphere; it is colorless, 
and a little lighter than the air; the specific gravity of 
air being 1.0000, that of nitrogen is .9736. It is not a 
supporter of combustion, and its negative qualities are 
so gracefully given by Professor Faraday in his lectures 
on "The Chemical History of a Candle," that I quote: 
"This other part of the air is by far the larger portion, 
and it is a very curious body when we come to examine 
it: it is remarkably curious, and yet you say, per- 
haps, that it is very uninteresting. It is uninteresting 
in some respects because of this, that it shows no bril- 
liant elfects of combustion. If I test it with a taper as 
I do oxygen and hydrogen, it does not burn like hydro- 
gen, nor does it make the taper burn like oxygen. Try 
it in any way I will, it does neither the one thing nor 
the other; it will not take fire; it will not let the taper 
burn; it puts out the combustion of everything. There 
is nothing that will burn in it in common circumstances. 
It has no smell; it is not sour; it does not dissolve in 
water; it is neither an acid nor an alkali; it is as indif- 
ferent to all our organs as it is possible for a thing to be. 
And you might say, 'It is nothing; it is not worth 
chemical attention; what does it do in the air?' 



28 COMBUSTION OF COAL. 

"Ah ! then come our beautiful and tine results shown 
by an observant philosophy. Suppose, in place of having 
nitrogen, or nitrogen and oxygen, we had pure oxygen as 
our atmosphere ; what would become of us ? You know 
very well that a piece of iron lit in a jar of oxygen goes 
on burning to the end. When you see a fire on an iron 
grate, imagine where the grate would go to if the whole 
of the atmosphere were oxygen. The grate would burn 
up more powerfully than the coals; for the grate itself 
is even more combustible than the coals which we burn 
in it. A fire put into the middle of a locomotive would 
be a fire in a magazine of fuel, if the atmosphere were 
oxygen. The nitrogen lowers it down and makes it 
moderate and useful for us, and then, with all that, it 
takes away with it the fumes you have seen produced 
from the candle, dispenses them throughout the whole 
of the atmosphere, and carries them away to places 
where they are wanted to perform a great and glorious 
purpose of good to man, for the sustenance of vegeta- 
tion, and thus does a most wonderful work, although 
you say, on examining it, ' why, it is a perfectly indif- 
ferent thing.' This nitrogen in its ordinary state is an 
active element; no action short of the most intense 
electric force, and then in the most infinitely small 
degree, can cause the nitrogen to combine directly with 
the other element of the atmosphere, or with things 
round about it; it is perfectly indifferent, and therefore 
to say, a safe substance." 

It will be seen from the above that nitrogen plays 
no active part whatever in combustion — it is simply the 



OXYGEN. 



29 



vessel, so to speak, in which the oxygen is delivered; 
the delivery having been made the vessel is no longer 
of any value in that connection, but the delivery is 
made in the body of incandescent fuel, and after its 
separation from the oxygen it passes on through the 
lire, and by virtue of its lighter gravity assists in main- 
taining a good draught, a matter of prime importance 
in furnace combustion. 

isTitrogen combines with oxygen to form five distinct 
compounds, as below : 

Table III. 





SYMBOL. 


COMPOSITION. 


NA"ME. 


WEIGHT. 


VOLUME. 




NITROGEN. 


OXYGEN. 


NITROGEN. 


OXYGEN. 


Nitrogen monoxide.... 


N 2 


28 


16 


2 


1 


Nitrogen dioxide 


N 2 2 


28 


32 


2 


2 


Xitrogen trioxide 


N 2 3 


28 


48 


2 


3 


Nitrogen tetroxide 


N, O t 


28 


64 


2 


4 


Nitrogen pentoxide.... 


N 2 Oa 


28 


80 


2 


5 



Oxygen is somewhat heavier than the air, having a 
specific gravity of 1.1056, air being 1.0000. It is the 
most abundant of all the elements : it forms eight-ninths 
of water; nearly one-fourth of air; and about one-half 
of silica, chalk and alumina ; the three most plentiful 
constituents of the earth's surface. Oxygen when free 
or uncombined is known only in the gaseous state. 
Numerous attempts have been made to reduce it to a 



30 COMBUSTION OF COAL. 

liquid or solid state, but so far the efforts have been 
fruitless. 

Oxygen when pure is colorless, tasteless and ino- 
derous. It combines with every known substance 
except fluorine. It is essential to the support of animal 
life, and is the sustaining principle of all the ordinary 
phenomena of combustion; and there are few experi- 
ments more brilliant than the burning of phosphorus, 
carbon or iron, in this gas, the products in each case 
being oxydized compounds of the substances burned. 
The weight of any compound will be found to be in all 
cases equal to the weight of the body burned, added to 
the weight of the oxygen required to effect the change. 

The Physical Properties of the Atmosphere (25)* — 
"Air, although essentially an invisible substance, has 
weight. A room the size of Westminster hall con- 
tains as much as seventy-rive, tons of air. The atoms 
of the air are of a minuteness that is perhaps quite 
inconceivable by the human mind. They are much 
smaller than the minutest molecules that can be made 
visible by the microscope, and have a breadth of about 
the -— ^ in- They exist in what is termed the gaseous 
state, which means that, small as they are, they float 
many of their own diameters asunder, from which it 
arises that air is compressible by the application of 
mechanical force. By a pressure of fifteen lbs. upon 
each square inch, air is reduced to half its previous 
bulk, although water, by the same pressure, is only 
compressed the ^^ part. Mariotte and Boyle have 

*From a lecture by Dr. Maim, London. 



WEIGHT OF THE ATMOSPHERE. 31 

established the law that every time the pressure upon 
air is doubled its volume is halved. This is the obvious 
reason why the air is more rare and light, bulk for bulk, 
at the higher regions of the atmosphere, than it is near 
the surface of the earth. Bat it is also expanded by 
increase of temperature, and this also by a fixed law r , 
which is, that air is increased in volume -\ 9 - part for each 
degree Fahr.; one thousand cubic inches at freezing tem- 
perature are increased to 1366.5 inches at the boiling 
point. The rarefaction of the atmosphere with ascent 
toward the higher regions is also affected according 
to a hxed law ; at a height of three miles the air lias a 
doubled volume and half its original density; it is 
again doubled in volume at about six miles high. It 
is probable that no animal could continue to live and 
breathe at a height of eight miles. The actual outer 
limit of the atmosphere is not certainly known. 

" Weight of the Atmosphere — The weight of the entire 
atmosphere was first demonstrated by Torricelli when 
he made his memorable invention of the barometer. 
It amounts to the same as the weight of a column of 
mercury of the same diameter, thirty inches high. But 
mercury is eleven thousand times heavier than an equal 
bulk of air. There is nearly one ton weight of air on 
each square foot of the ground. The atmosphere 
amounts to about the - X2 ^ Q part of the weight of the 
entire earth. Air, however, presses in all directions as 
w r ell as down. The air is really composed of two dif- 
ferent kinds of gasses, which mingle without interfer- 



32 COMBUSTION OF COAL. 

ing with each other by pressure. Each is, as it were, 
a vacuum to the other. 

" Vapor — The vapor of water rises into the inter- 
spaces of these aerial atoms in a similarly free and 
.unconstrained way; hut more of it can be sustained in 
warm air than in cold. Air at a temperature of 32° 
can sustain the -^- part of its own weight of aqueous 
vapor, but at 86° it can sustain -^ part of its own 
weight. The barometer gives the combined weight of 
the oxygen, nitrogen, and gaseous vapor of the air, and 
the portion of this weight which is due to aqueous va- 
por is called the elastic force of vapor. With a barom- 
eter standing at 30.000 inches, and with a hygrometer 
indicating an elastic force of vapor of 0.450, very nearly 
one-quarter lb. of the entire pressure of fifteen lbs. on 
each square inch is due to the vapor. When more 
vapor is generated than can be at once carried away, 
the barometer necessarily rises ; when vapor is con- 
densed in the atmosphere, the barometer falls; when 
the temperature of saturated air is reduced from 80° to 
60°, five grains of aqueous vapor are deposited from 
each cubic foot. This is the effective cause of rain. 
Warm air drinks up vapor and carries it away, and 
subsequently deposits it when it comes to some region 
where it gets chilled. 

"The Temperature of the air decreases with height, 
about 1° for each three hundred feet or four hundred 
feet ascended; this is because the air gets further from 
the source of heat, and also because heat is absorbed 



CARBONIC ACID. 38 



above to maintain the expansion of the air. Sensible 
heat is lost on the expansion of air, and is produced 
on its condensation. Pure air is virtually quite per- 
vious to heat; none stops in the air, but all passes 
through. Aqueous vapor, on the other hand, acts as- 
a screen to heat. Prof. Tyndall has shown that ten per 
cent, of the solar heat radiated from the earth through 
a moist atmosphere is stopped within ten feet of the 
ground. The absolute diathermancy of dry air ac- 
counts for the scorching heat of mountain tops, as the 
retentive power of aqueous vapor does for the soft heat 
of low lying regions in the tropics. The rain deluges 
of equatorial calms are due to the radiation of heat 
through the upper dry layers of the atmosphere. 
Cumuli clouds are formed from the same cause; they 
are the capitals of invisible columns of saturated air. 
Mountain tops are condensers of moisture for a similar 
reason. 

" Carbonic Acid — There is in air, besides the aqueous 
vapor, 3.36 parts in every ten thousand of carbonic 
acid gas, and three and a-half parts in every ten mill- 
ions of ammonia. Small as these quantities appear, 
they are sufficient to produce very astonishing results; 
there are one million three hundred thousand tons of 
carbonic acid, containing three hundred and seventy- 
one thousand four hundred and seventy-five tons of 
carbon in the air, which rests upon each square mile 
of the earth, and thirty lbs. of ammonia are carried 
down by the rain to each acre of land every year. 
(4) 



34 COMBUSTION OP COAL. 

" Ozone — There is one part of ozone in every seven 
hundred parts of air; but this ozone is in reality only 
a condensed form of oxygen itself; three volumes of 
oxygen are condensed to form two volumes of ozone. 
It is oxygen in an increased state of activity. 

" The Diathermancy and Transparency of the air are 
both of the very highest importance to the life existing 
upon the earth. It is its diathermancy which enables 
the sun's heat to reach the terrestrial surface for the 
performance of its marvelous operations. It is its trans- 
parency which renders the air the window of the earth, 
giving man his outlook into space and admitting the 
wonderful effects of color and light. If the air were 
not transparent, all nature would be in a perpetual 
dense fog. The blueness of the sky is due to the weak 
blue rays of light being arrested by the air and its 
transparent vapors, and turned back upon the earth. 
The brilliant sun-set colors are similarly due to- the 
arrest and reflection of the stronger yellow and red 
vibrations, by the denser vapors of the clouds." 



CHAPTER III. 



FUELS. 



Classification of Fuel — Wood — Water Present in Wood — Composi- 
tion of Wood — Wood Charcoal — Combustibility of Wood 
Charcoal — Peat — Analysis of Peat — Products of the Distilla- 
tion of Peat — Peat as a Fuel — Peat Charcoal — Lignite — Differ- 
ence between Lignite and Brown Coal — Lignite as a Fuel — 
Water in Lignite — Analysis of Lignites — Classification of Coal 
— Bituminous Coal — Analysis of Bituminous Coals — Non-caking 
Coals — Block Coal — Caking Coals — Gas Coal — Coke — The Influ- 
ence of Temperature and Pressure in the yield of Coke — Can- 
nel Coal — Semi-bituminous Coal — Semi-anthracite Coal — 
Anthracite Coal. 

Fuel is a word employed to express, in general 
terms, any substance which may be economically burned 
by means of atmospheric air to generate heat. The 
economic value of any fuel will depend upon its heating 
power. The two elements contributing this property 
to fuel are carbon and hydrogen. The more impor- 
tant varieties of fuel include wood, peat, lignite and 
coal. These are classed by Dr. Percy as follows : 

Classification of Fuels. 
Wood. 

Peat. 

Lignite. 



Coal. 



{Non-caking, rich in oxygen. 
Caking. 
Non-caking, rich in carbon. 



36 



COMBUSTION OF COAL. 



Carbonization. 
Products of 



Solid. 



I 

[ Volatile. 



f Wood — charcoal. 
■j Peat — charcoal. 
{ Coke. 

{Carbonic Oxide. 
Hydrogen. 
Hydro-carbon. 



Wood, as a fuel, may be divided into two classes, 
hard and soft. 

Hard woods include compact, heavy woods — like 
oak, hickory, beech, elm, ash, walnut. 

Soft woods include pine, birch, poplar, willow. 

Freshly cut green wood contains on an average 
about forty-five per cent, of moisture, often more, 
though sometimes less; and after long exposure to the 
atmosphere under favorable conditions it still retains 
from eighteen to twenty per cent, of moisture. This is 
a point of great practical importance in reference to the 
direct application of wood as fuel. The following table, 
prepared by M. Yiolette, shows the proportion of water 
expelled from wood at gradually increasing tempera- 
tures ; 

Table IV. 



TEMPERATURE. 


WATER EXPELLED FROM ONE HUNDRED 
PARTS OF WOOD. 




OAK. 


ASH. 


ELM. 


WALNUT. 


257° Fahr 


15.26 
17.93 
32.13 
35.80 
44.31 


14.78 
16.19 
21.22 
27.51 

33.38 


15.32 

17.02 

36.94? 

33.38 

40.56 


15.55 


302° Fahr 


17.43 


347° Fahr 


21.00 


392° Fahr 


41.77? 


437° Fahr 


36.56 







THE COMPOSITION OF WOOD. 



37 



The wood which. M. Violette operated upon had 
been kept in store during two years. 

In each experiment the specimens were exposed 
during two hours to dessication in a current of super- 
heated steam, of which the temperature was gradually 
raised from 257° to 437° Fahr. When w^ood, which has 
been strongly dried by means of artificial heat, is left 
exposed to the atmosphere, it re-absorbs about as much 
water as it contains in its air-dried state. 

Table V — Showing The Composition of Wood. 

ANALYSIS BY M. EUGENE CHEVANDIER. 




Where wood is protected from the atmosphere and 
heated to about 600° Fahr., its gaseous or volatile 
elements are driven off, and a fixed residue called char- 
coal remains. 

Good charcoal is black; gives a sonorous ring when 
struck; breaks with more or less conchoidal fracture; 
is easily pulverizable, but does not crumble under mod- 



38 



COMBUSTION OF COAL. 



erate pressure; floats on water, and does not burn with 
flame when ignited in separate pieces. 

Table VI — Showing the Composition of Charcoal Produced at 
Various Temperatures (2). 

BY M. YIOLETTE. 



TEMPERATURE 

OF 

CARBONIZATION. 



FAHRENHEIT. 



302° 



392* j 

482 

572..... 

662 

810 

1873 

2012 

2282 

2372 

2732 



Melting point of) 



platinum. 



COMPOSITION OF THE SOLID PRODUCT. 


CARBON. 


HYDROGEN 


OXYGEN, 
NITROGEN 
AM) LOSS. 


ASH. 


PER CENT. 


PER CENT. 


PER CENT. 


PER CENT. 


47.51 


6.12 


46.29 


0.08 


51.82 


3.99 


43.98 


0.23 


65.59 


4.81 


28.97 


0.63 


73.24 


4.25 


21.96 


0.57 


76.64 


4.14 


18.44 


0.61 


81.64 


4.96 


15.24 


1.61 


81.97 


2.30 


14.15 


1.60 


83.29 


1.70 


13.79 


1.22 


88.14 


1.42 


9.26 


1.20 


90.81 


1.58 


6.49 


1.15 


94.57 


0.74 


3.84 


0.66 


96.52 


0.62 


0.94 


1.95 



O © 
fc 53 H 

b o a o 



PER CENT. 



47.51 

39.88 
32.98 
24.61 
22.42 
15.40 
15.30 
15.32 
15.80 
15.85 
16.36 
14.47 



The wood experimented on was that of black alder 
or alder buckthorn, which furnishes a charcoal suitable 
for gunpowder. 

Combustibility of Wood-charcoal — M. Violette states 
that charcoal made at 500° Fahr. burns most easily; and 
that made between 1832° and 2732° Fahr. can not be 

* The products obtained at these temperatures can not properly be termed 
charcoal. 



PEAT OR TURF. 39 



ignited like ordinary charcoal. Charcoal made at a 
constant temperature of 572° Fahr. takes fire in the air 
when heated to between 680° and 716° Fahr., according to 
the nature of the wood from which it has been derived; 
charcoal from light woods, other things he equal, ignit- 
ing most easily. 

Peat or Turf — Peat is composed of various kinds 
of plants which are undergoing a gradual tran> ma- 
tion by a process of slow burning or carbonization, in 
which the oxygen of the plants is being liberated under 
special conditions of moisture and heat, leaving a 
spongy carbonaceous mass, in which the remains of the 
plants are often so well preserved that species may 
easily be distinguished. The ormation of peat may be 
regarded as one of the most important geological 
changes now in evident progress. Immense accumula- 
tions of peat exist in various parts of the world. 
Within two miles of South Bend, Indiana, is the eastern 
terminus of one of the most extensive peat beds known, 
(4) being three miles in width and extending westward 
down the valley of the Kankakee for more than sixty 
miles, varying from five to fifty feet in thickness. 

In color, peat varies from a yellowish-brown through 
all gradations to a very dark brown, almost black. The 
former in structure is light, spongy and fibrous; the 
latter is more compact and pitchy in its appearance, the 
fibrous texture being almost entirely obliterated. In 
advanced stages of decomposition it is compact and 
dense, presenting an earthy fracture when broken; in 
general the darker the peat the richer it is in carbon. 



40 



COMBUSTION OF COAL. 



Peat formations are confined to cold and temperate 
climates, and swampy ground. In its natural and more 
advanced state, peat contains about three-fourths of its 
own weight of water; in the earlier stages of decompo- 
sition the quantity of water present often amounts to as 
much as ninety per cent, of the whole weight, and is 
totally unfit for any of the purposes for which fuel is 
employed. 

Very little use has been made of peat in this country, 
owing to the abundance, cheapness and superior heat- 
ing power of coal. In Ireland, Germany, Sweden and 
other foreign countries, it is used largely not only for 
domestic, but for metallurgical purposes. 

The following analysis of Irish peat is upon the 
authority of Sir Robert Kane : 



Table VII — Chemical Composition of Irish Peat (2). 

PERFECTLY DRY. 



DESCRIPTION AND LOCALITY 
OF PEAT. 




o 

o 
« 


K 

o 

o 
« 


w 
o 


i. 

H 

O 
« 


X 

CO 

< 




.405 
.609 
.335 
.055 
.500 
.280 
.853 


PER 
CENT. 

57.52 
58.50 
5S.30 
50.34 
5S.G0 
58.53 
59.42 


PER 

CENT. 

G.S3 
5.91 
6.43 
4.81 
0.5.3 
5.73 
5.49 


PER 
CENT. 

32.23 
31.40 
31.36 
30.20 
30.50 
32.32 
30.50 


PER 

CENT. 

1.42 
0.85 
1.22 
0.74 
1.84 
0.93 
1.64 


PER 
CENT. 

1.99 




3.30 


3. Light surface, Wood of Allen 


2.74 


4. Compact and dense, Wood of Allen... 


7.90 
2.63 


6. Light fibrous, Upper Shannon 

7. Very dense, compact, Upper Shan'on 


2.47 
2.97 




.528 


58.18 


5.96 


31.21 


1.23 


3.4;'. 







\ 



DISTILLATION OF IRISH PEATS. 



41 



Table VIII — Showing the Products of Distillation of the Irish 
Peats given in Table No. VII. 



DESCRIPTION AND LOCALITY OF 
PEAT. 


AVATER. 


CRUDE TAR. 


CHARCOAL. 


GAS. 


Nos. 1 and 2, Philipstown 

No. 3, Wood of Allen 


PER CENT. 

23.6 
32.3 
38.1 
33.6 

38.1 
21.8 


PER CENT. 

2.0 
3.6 
2.8 
2.9 
4.4 
1.5 


PER CENT. 
37.5 
39.1 

32.6 
31.1 

21.8 
19.0 


PER CENT. 

36.9 
25.0 


No. 4, Wood of Allen 


26.5 


No. 5, Tickneven 


32.3 


No. 6, Upper Shannon 

No. 7, Upper Shannon 


35.7 

57.7 






Averages 


31.4 


2.8 


29.2 


36.6 







The tar, when re-distilled, yielded water, paramne, 
oils, charcoal and gas. 

The water yielded chloride of ammonium, acetic 
acid and wood-spirit. 

In a French report on the use of peat as a fuel for 
locomotives, after experimenting on a large scale, the 
conclusion was reached that an economy of nearly one- 
half might he effected over a similar mileage and ton- 
age with coal; setting aside the greatly reduced injury 
to hoilers, flues and grates. It is also claimed for peat 
in this report that, the firing once understood, is much 
more easily managed than coal ; requiring no stoking ; 
the heat being more regular, and not subject to the sud- 
den changes in intensity that occur so frequently with 
coal and coke, and which changes injure the furnaces. 



42 COMBUSTION OF COAL. 

Peat Charcoal — The charcoal produced by the car- 
bonization of ordinary air-dried peat is very friable and 
porous; it takes fire very readily, and when ignited 
nearly always continues to burn until its carbonaceous 
matter is wholly consumed; it scintillates in a remarka- 
ble degree when burned in a smith's fire ; its extinction 
when in mass is difficult, and hence this is the trouble- 
some part of its manufacture by the usual method of 
carbonization in piles; and it is so little coherent that 
it can not be conveyed without much of it being 
crushed to dust (20). 

Lignite — Is classed among mineral coals, and occu- 
pies a position historically between peat and bituminous 
coal. It is not synonymous with brown coal, proper, 
though there are many points of similarity. It is believed 
to be of later origin than bituminous coal and is in a less 
advanced stage of decomposition; the woody -fibre and 
vegetable texture of lignite is almost entirely wanting 
in coal, though there is little doubt that they are of one 
common origin. The chemical difference between lignite 
and brown coal may be determined by dry distillation, 
in which the former yields acetic acid, and acetate of 
ammonia, whereas, coal produces only ammonical liquor 
(5). Woody fibre gives rise to acetic acid; lignite 
must, therefore, still contain undecomposed woody fibre. 
Lignite and brown coal belong chiefly to the cretaceous 
and tertiary periods. Lignite varies considerably in 
appearance and structure, usually, however, preserving 
a wood-like appearance when broken, the fracture is 
uneven presenting a brown to a very dark brown-black 



LIGNITE. 43 



color, with a dull and frequently a fatty lustre. It 
easily breaks or crumbles in handling, and will not bear 
rough transportation to great distance; neither will it 
bear long continued exposure to the weather; crumbling 
rapidly. 

It can be coked but the coke is not of good quality, 
though some lignites coke better than others. 

As a fuel it must be used in its natural state, and 
near where it is mined, to obtain the best results. It 
will be noticed in examining the annexed tables that it 
contains a large per cent, of volatile matter and water. 
It may be deprived of this water by heating the lignite 
above the boiling point of water, but if a piece so heated 
is afterwards allowed to remain in the open air it will 
again absorb from the atmosphere the same quantity of 
water as that driven off by the heat. 

It is non-caking in the fire, and yields but a mod- 
erate heat, that is, its heating power in general is below 
that of ordinary bituminous coals. 

The number of units of heat in lignite of different 
qualities and from different parts of the world are 
given in the tables, and its relative heating power may 
be easily determined as compared with coal of a known 
calorific value. It must not be forgotten in making use 
of the figures in the columns of units of heat in these 
tables, that it is the theoretical numbers which are given 
after the water in the specimen had been expelled by 
heat, the quantity of heat so expended in its evapora- 
tion does not appear in the calculation. 



44 COMBUSTION OF COAL. 

Lignite contains from ten to twenty per cent, of 
water, which must be evaporated in the fire before any 
useful effect is obtained, and, at a considerable loss, so 
this must be taken into account in any comparison 
made with other fuels. 

The use of lignite in this country is so limited that 
it has at present little or no commercial value except in 
the immediate vicinity where it is mined; but as the 
vast territories west of the Mississippi are developed it 
will then become a matter of growing importance, as 
lignite must become their chief fuel, after the disap- 
pearance of the forests. Very extensive deposits occur 
in California, Colorado, Nevada, Utah, Wyoming, New 
Mexico, Oregon and Alaska. 

Kentucky — Lignite from the bluff of Fort Jefferson, 
Ballard county, Kentucky. 

PROXIMATE ANALYSIS BY PROFESSOR E. T. COX. 

Specific gravity 1 . 201 

PER CENT. 

Fixed carbon 40. 

Volatile combustible matter 23. 

Water 30. 

Ash, reddish yellow or flesh tint 7. 

100. 

Total volatile matter 53. percent. 

Coke, reduced in bulk and nearly the 

same shape as the original specimen 47. per cent. 

100. 
Some of this lignite has very much the appearance 
of coal; hence, it is apt to be mistaken for it; but it 



LIGNITE. 45 



is of much more recent date than true coal, and has 
been formed under entirely different circumstances, and 
derived from a very different vegetation than that which 
nourished during the carboniferous era. 

Washington Territory — A sample of BilliDgham Bay 
coal, Washington Territory, was sent by Dr. John Evans 
to Professor E. T. Cox, who made both proximate and 
ultimate analyses of it, with results as given below : 

PROXIMATE ANALYSIS. 

PER CENT. 

Fixed carbon 58.25 

Volatile combustible matter 31.75 

Water 7.00 

Ashes, reddish brown 3.00 

100.00 

Coke 61.25 per cent. 

Volatile matter 38.75 per cent. 

The coke slightly shrunken, dull black. 

This is to be regarded as lignite rather than a true 
coal ; it may be handled without much loss, has a bedded 
structure; layers about one -eighth inch thick, sometimes 
denned by a thin scale of carbonate of lime. Color, 
glossy black; fracture, slaty and parallel to stratification, 
in the opposite direction the fracture is irregular and 
brittle. This formation has much less earthy matter 
than most tertiary coals or lignites, and much more 
carbon. 



ULTIMATE ANALYSIS. 

FIRST SAMPLE. PER CENT. 

Carbon 68.454 

Hydrogen 6.666 

Sulphur 1.000 



46 COMBUSTION OF COAL. 

Water (at 212°) 7.000 

Ashes 3.400 

Oxygen, nitrogen and loss 13.480 

100.000 

SECOND SAMPLE. PER CENT. 

Carbon 67.090 

Hydrogen 4.555 

Sulphur 1.000 

Water (at 212°).. 7.000 

Ashes 3.100 

Oxygen, nitrogen and loss 17.3p5 

100.000 
This coal (or lignite) contains a large amount of 
oxygen and is deficient in the amount of hydro-carbons, 
and therefore, more difficult of ignition than most of 
the western bituminous coals, but it is rich in fixed car- 
bon in the coke and will therefore be a durable coal. 
It is intermediate in composition of its ultimate elements 
to cannel coal and lignites. 

Vancoover's Island — Lignite, color, dull black, sub- 
metallic; fracture, foliated and slaty, numerous partings 
filled with scales of carbonate of lime. 

PROXIMATE ANALYSIS BY PROFESSOR E. T. COX. 

PER CENT. 

Fixed carbon 62. 

Volatile combustible matter 31. 

Water 4. 

Ash, reddish brown 3. 

100. 

Coke 65 per cent. 

Volatile matter 35 per cent. 



LIGNITE. 47 



This lignite shrinks slightly in coking, and is dull 
black in color. 

Colorado — Lignite from Carbon City on the Union 
Pacific Railroad. Specimen brought by Edward King. 

ANALYSIS BY PROFESSOR E. T. COX. 

Color, jet black — specific gravity 1.271 

Weight, one cubic foot 80.68 lbs. 

PER CENT. 

Fixed carbon 41.25 

Volatile combustible matter 46.00 

Water 3. .50 

Ash, lead color 9.25 

• 

100.00 

Coke 50.50 per cent. 

Volatile matter 49.50 per cent. 

Coke — shrivelled, cracked, lusterless. 

Colorado — Lignite from Canon City, about two hun- 
dred miles south of Denver City. 

PROXIMATE ANALYSIS BY PROFESSOR E. T. COX. 

Color, jet black — specific gravity 1.279 

Weight, one cubic foot 79.23 lbs. 

PER CENT. 

Fixed carbon 56.80 

Volatile combustible matter 34.20 

Water 4.50 

Ash, ochre yellow 4.50 

100.00 

Coke 61.30 per cent. 

Volatile matter 38.70 per cent. 

Coke — slightly swollen, unchanged, semi-lustrous. 

This is a good fuel. 



48 COMBUSTION OF COAL. 

Arkansas — Lignite from Ouachita county. This lio-- 
nite has a rather rhomboidal cleavage; can he cut with 
a knife, and receives a good polish, which gives it a 
much "blacker appearance. It is solid, heavy, compact, 
of a hluish-hrown color, disintegrating, however, by 
exposure to the atmosphere. 

PROXIMATE ANALYSIS BY PEOFESSOE E. T. COX. 

PER CENT. 

Fixed carbon 34.50 

Volatile combustible matter 28.50 

Water (at 260°) 32.00 

Ashes 5.00 

100.00 

Coke 39.5 per cent. 

Volatile matter 60.5 per cent. 

This lignite was distilled in a small iron crucible, to 
which a glass receiver was attached and kept cool with 
water. The first product that came over was gas hav- 
ing a feeble odor of sulphurous acid and burning with a 
tolerably bright flame. The gas was soon accompanied 
by ammoniacal water, a yellowish oil, and a waxy pro- 
duct; the latter rising into the exit pipe of the glass 
receiver whenever the fire was a little too strong, which 
proves it to be very volatile; but when condensed, it has 
the consistency of lard, and the color of beeswax. The 
last products which came over were lubricating oil and 
paraffin e. 

Three thousand seven hundred grains of this lignite 
gave: 



LIGNITE. 49 



GRAINS. PER CENT. 

Coke 1,400 37.83 

Watery solution, containing sulphurous 

acid, organic acids, and ammonia.... 1,270 34.32 

Crude oil 450 12.16 

Gas and loss 580 15. G9 

3,700 100.00 

From this analysis two thousand pounds of lignite 
would yield 35.40 gallons crude oil. 

Occasionally small segregations are found in the 
lignite, approaching amber and retin-asphaltum ; in 
fact, much of the coal has a retin-asphaltum aspect. 

Kentucky — Brown coal (lignite?), sample from one 
and a-half miles north-west of Blandville, Ballard 
countv. 



PEOXIMATE ANALYSIS BY PROFESSOR E. T. COX. 

Specific gravity, 1.173. 

PER CENT. 

Fixed carbon 31.0 

Volatile combustible matter 48.0 

Water 11.5 

A sh , w h i t e 9.5 

100.00 

Coke 40.5 per cent. 

Volatile matter 59.5 per cent. 

This coal contains from twenty to thirty per cent- 
less fixed carbon than the coals of the carboniferous 
epoch, and usually a much larger quantity of hygro- 
metric moisture, which renders them inferior as fuel 
and still less applicable for the generation of steam, and 
manufacturing purposes generally. 
(5) 



50 COMBUSTION OF COAL. 

A specimen from Robertson county, Texas, taken 
from a seam ten feet thick, was analyzed, and is described 
by Professor E. T. Cox (4), as a lusterless, dull brown 
coal with irregular fracture and much inclined to shrink, 
crack and fall to pieces on exposure to the air. It con- 
tained by proximate analysis, 

PER CENT. 

Fixed carbon. 45.00 

Gas 39.50 

Water.... 11.00 

Ash, white 4.50 

100.00 

Coke 49.50 per cent. 

Volatile matter 50.50 per cent. 

Heat units 13,068 

Specific gravity 1.232 

Weight of one cubic foot 77 lbs. 

Coke— slightly shrunken, lusterless, and bears a close 
resemblance to wood charcoal. 



LIGNITE. 



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52 



COMBUSTION OF COAL. 



CLASSIFICATION OF COAL. 

Coals are classified according to the amount of car- 
bon and volatile matter present in their composition : 
the following is the classification adopted by Professor 
H. D. Rogers, in the "Geology of Pennsylvania": 



Anthracites. 



f Hard Anthracites. 

] Semi or Gaseous Anthracites. 



Common 
Bituminous 
Coal 



Bituminous 
coal 



I 



Semi-bitumin- f Semi-bituminous cherry coal, and 
ous coals j Semi-bituminous splint coal. 

[ Caking coal. 

; Cherry coal. 

[ Splint coal. 

( Cannel coals. [hill, etc.) 

Hydrogenous or Gas coals J Hydrogenous Shaly coal (Torbane- 

{ Asphaltic coal (Albert Mine.) 

Bituminous Coal — When coal contains as much as 
eighteen or twenty per cent, of volatile combustible 
matter it is called bituminous. The passage of lignite 
into bituminous coal is as gradual as that of bituminous 
coal into anthracite, so there is no precise line of 
demarkation between these classes of coal. Some bitu- 
minous coals yield upon analysis as much and occa- 
sionally more than fifty per cent, of volatile matter. It 
may be said, however, to range from twenty to fifty per 
cent., and will hardly admit of averaging, as scarcely 
any two mines yield coal of the same quality. The 
amount of volatile matter in bituminous coal can not 
be judged from its appearance simply, and perhaps the 
easiest and best way to arrive at it, and to determine 



BITUMINOUS COAL. 53 



the amount of fixed carbon at the same time, is by 
proximate analysis. 

The use of the word bituminous is somewhat mis- 
leading: there is no bituminous coal in this country, 
which contains any bitumen in its composition. In 
general, this word is applied to such coals as have a 
large proportion of organic elements in addition to its 
tixed carbon, and includes all the hydro-carbons, water 
and nitrogen, in its composition. 

The true bitumens are destitute of organic structure ; 
they appear to have arisen from coal or lignite by the 
action of subterranean heat, and very closely resemble 
some of the products yielded by the destructive distilla- 
tion of those bodies. They are very numerous, and 
have yet been but imperfectly studied. 

It is possible that its name has been applied to coal 
on account of a similarity between the burning of a 
coal rich in hydro-carbon and bitumen. The latter is 
very inflammable, and burns with a red, smoky flame. 

Professor Rogers, in his Geology of Pennsylvania, 
makes a distinction between what he calls common bitu- 
minous coals and hydrogenous or gas coals. His scheme 
of classification will be found on page 52. It is scarcely 
possible to give in a single description the physical prop- 
erties of bituminous coal, which will be applicable to all 
varieties. 

In external properties, (23) the common bituminous 
coals range in color from a pitch black to a dark brown; 
their luster is vitreous, resinous, or, in the more fibrous 
varieties, silky ; their structure is compact or cuboidal, 



54 COMBUSTION OF COAL. 

slaty, columnar, and even fibrous; and their fracture, 
irrespective of structural joints and cleavage, is con- 
ehoidal, and often flat and rectangular, and sometimes 
fibrous. It is distinctive of these coals to burn with 
more or less of yellow bituminous flame and smoke, and 
to emit, when burning, a bituminous odor. In 'proxi- 
mate composition— namely, in fixed carbon or coke, vola- 
tile matter or combustible gases, and earthy sediment- 
ary residue or ashes — they may be regarded as ranging 
between the following general limits : 

Fixed carbon from 52 to 84 per cent. 

Volatile matter from 12 to 48 per cent. 

Earthy matter.... from 2 to 20 per cent. 

Sulphur.... .... ...from 1 to 3 per cent. 

Dried at a temperature of 212° Fahr., the yield of 
water is from one to three or four per cent. 

The proportion of earthy matter is of course too 
variable to have a maximum limit affixed to it 3 as all the 
kinds of coal may, by impurities, graduate into carbona- 
ceous shales. 

In ultimate composition, the coals of this class may be 
recorded as ranging approximately nearly thus — 

Carbon 75 to 80 per cent. 

Hydrogen 5 to 6 per cent. 

Nitrogen 1 to 2 per cent. 

Oxygen 4 to 10 per cent. 

Sulphur 0.4 to 3 per cent. 

Ash 3 to 10 percent. 



BITUMINOUS COAL. 55 



Composition of Various Bituminous Coals. 

ILLINOIS. 

Smith's, Warren county. Dr. Xorwoocl. 

PER CENT. 

Fixed carbon 51.7 

Volatile matter 43. 1 

Earthy matter 5.2 

100.0 
Ashes, red. 

Specific gravity, 1.24. 

Montauk Coal — A compact, deep black, caking coal, 
laminse very indistinct, breaks into irregular cubes, and 
contains some pyrites. E. T. Cox. 

PER CENT. 

Fixed carbon 48.00 

Gas 35.00 

Water 11.50 

Ash, brown 5.50 

100.00 

Coke 53.50 

Heat, units 12,760 

Specific gravity 1.232 

Weight of one cubic foot 77 lbs. 

Coke: puffed, lusterless, amorphous. 

Bureau county, Illinois. Dr. V. Z. Blancly. 

PER CENT. 

Fixed carbon 57.6 

Volatile matter 28.8 

Moisture 11.2 

Ash, nearly white 2.4 

100.0 
Coke — Close, not swollen. 

Specific gravity, 1.316. 

Weight of a cubic foot 80 lbs. 



56 COMBUSTION OF COAL. 

The heat units in this coal, determined as below, are : 

Carbon 576 X 14,544= 8,377 

Volatile matter 288 X 20,115 = 5,793 

Less 288 X 3,600= 1,037 4,756 

Total heat units 13,133 

Mercer county, Illinois. Dr. V. Z. Blandy. 

PER CENT. 

Fixed carbon 54.8 

Volatile matter 31.2 

Moisture 8.4 

Ash, fawn color 5.6 

100.0 
Coke — pulverulent between the fingers. 

Specific gravity, 1.259. 

Weight of a cubic foot 78.49 lbs. 

Heat units s 13,123 

INDIANA. 

McClellan and Zellers' Coal, north of Brazil, Clay 
county. This is a typical block coal, a dull, lusterless 
black, in thin laminae, separated by fibrous charcoal 
partings, very strong across the bedding, lines, free from 
pyrites and calcite, and is highly esteemed for blast and 
puddling furnace use. The specimen analyzed was 
fresh from the mine and held a large excess of water 
which, on exposure to the air of the laboratory for a 
few weeks, would reduce to about 3.5 per cent. E. T. 
Cox. 

PER CENT. 

Fixed carbon 56.50 

Gas 32.50 

Water 8.50 



BITUMINOUS COAL. 



Ash, white 2.50 

100.00 

Coke 59.00 

Heat units, wet coal 13,588 

Heat units, dry coal 14,400 

Specific gravity 1 .285 

Weight of one cubic foot 80.31 lbs. 

Coke — laminate, not swollen, lusterless. 

INDIANA. 

Ellas Coojmder's Coal, near Middletown, Clay county. 
This is a compact, jet-black, slightly laminate, caking 
coal, with some evidence of pyrites in the lower part. 
E. T. Cox. 

TOP. MIDDLE. BOTTOM. 

Fixed carbon 44.00 45.00 50.50 

Gas 47.50 44.00 42.50 

Water 4.00 2.50 3.00 

Ash pink 4.50 brown 8.50 yellow 4.00 

Coke, percent 48.50 53.50 54.50 

Heat units 14,263 13,811 14,364 

Specific gravity 1.280 1.533 1.211 

Weight of one cubic foot 80.00 95.81 75.68 

Coke : Vitreous, puffed, amorphous. 

PENNSYLVANIA . 

Connellsville Coal, Fayette county. From this coal 
the celebrated foundry coke is made. The specimen 
received would measure about one-half a cubic foot; 
every part of it displayed prismatic colors ; it had a col- 
umnar structure, inclined to be granular, and easily 
broken into small fragments. E. T. Cox. 

PER CENT. 

Fixed carbon 65.00 

Gas 24.00 



58 COMBUSTION OF COAL. 

Water 4.50 

Ash, white 6.50 ' 



100.00 

Coke 71.50 

Specific gravity 1.28 

"Weight of one cubic foot 80.00 

Coke: Of steel gray color, columnar, very strong, 
dense, slightly puffed on the surface. 

The heat units in this coal are : 

PER CENT. 

Carbon 65X14,544= 9,454 

Volatile matter 24X20,115= 4,828 

Less 24X 3,600= 864 3,964 



Total* heat units 13,418 

Youghiogheny Coal, Pennsylvania. Geological sur 
vey of Kentucky. Professor Peter. 

PER CENT. 

Fixed carbon 58.40 

Volatile combustible matter 35.00 

Moisture 1.00 

Ashes 5.60 



100.00 
The heat units in this coal are : 

Carbon 584X14,544= 8,494 

Volatile matter 35X20,115= 7,040 

Less 35 X 3,600= 1,260 5,780 



Total heat units ,...14,274 

This is considered a very superior gas coal, and fur- 
nishes a quality of coke highly valued for domestic use. 

PENNSYLVANIA. 

Stone's Gas Coal, Fayette county. This coal is in 
common use in many cities in the western states for the 



BITUMINOUS COAL. 59 



manufacture of illuminating gas. The specimen analyzed 
was obtained at the Indianapolis gas works, and said, by 
the superintendent, to be first-class. E. T. Cox. 

PER CENT. 

Fixed carbon 58 

Gas 34 

Water 3 

A sh, white 5 

100 

Coke 63 per cent. 

Heat units 14,049 

Specific gravity 1 . 292 

Weight of one cubic foot 80.75 lbs. 

Coke: slightly puffed, amorphous, lusterless, and is 
much esteemed as a grate and stove fuel. 

KENTUCKY. 

Coal from Sardric and Mud river, Mecklenburg 
county. This is a dull black, vitreous, caking coal, with 
irregular, resinous fracture, laminae indistinct, no visible 
pyrites. E. T. Cox. 

SARDRIC. MUD RIVER. 

Fixed carbon 51.00 57.00 

Gas 42.50 37.00 

Water 2.00 • 3.50 

Ash, white 4.50 2.50 

Coke ... 55.50 59.50 

Heat units 14,436 14,400 

Specific gravity 1.325 1.280 

Weight of one cubic foot 82.81 lbs. 80.00 lbs. 

Coke : Puffed, lusterless, amorphous. 

OHIO. 

Coal from Nelsonville — From the Geological Eeport, 
1869. 



60 



COMBUSTION OF COAL. 



ANALYSIS BY PROF. T. 


Jr. WORMLEY. 








PORTION OF THE SEAM. 




BOTTOM. 


MIDDLE. 


TOP. 


Specific gravity 


1.285 


1.272 


1.284 








Water 


6.20 
31.30 

59.80 
2.70 


6.65 
33.05 
58.40 

1.90 


5.00 


Volatile matter 


32.80 


Fixed carbon 


53.15 


Ash - 


9.05 








Total 


100.00 


100.00 


100.C0 








Sulphur 


0.97 

Gray. 

Compact. 

3.56 


0.41 

Yellow. 

Compact. 

3.24 


94 


Color of ash 


Gray. 
Compact. 

4.95 


Nature of the coke 


Cubic feet of permanent gas 
of coal 


per pound 







An average of the above three samples gives, 

Volatile matter 3238 per cent. 

Fixed carbon 5712 per cent. 

Then, taking 14,544 as the heat units in carbon (as 
has been done in the preceding examples), and 20,115 as 
the heat units of the combustion of the combined vola- 
tile matter, deducting 3,600 units for the heat expended 
in their expulsion, we have, 

Carbon 5712X14,544= 8,308 

Volatile matter 3238X20,115= 6,513 

Less 3238X 3,600= 1,166 5,347 



Total heat units in one pound of coal 13,055 



GAS COAL. 61 



CLASSIFICATION OF BITUMINOUS COALS. 

It will serve our present purpose if we divide all 
bituminous coals into two classes : 

CAKING ANT) NON-CAKING. 

Caking coal is the name given to any coal which when 
heated the lumps seem to fuse together, and swell in size, 
having a pasty appearance and emitting a gummy or 
sticky substance over the surface, liberating small 
streams of gas which appear to escape from a considera- 
ble pressure from the interior of the coal, and which 
burn with a bright yellow and sometimes a reddish 
flame, terminating in smoke. A characteristic of cak- 
ing coal is that lumps, either large or small, being ren- 
dered pasty by the action of the heat, will cohere in the 
fire and form a spongy looking mass, which, not unfre- 
quently, covers almost the whole surface of the grate. 
This is the property called caking. Caking coals rich 
in hydro-carbons are highly esteemed by gas manufac- 
turers. 

Gas Coal — The following on the requisites of a gas 
coal is from the pen of Mr. James McFarlane: (18) 

a The most important requisites of gas coal are, first, 
that it contain a large amount of volatile combustible 
matter, or gas; second, that the volatile matter be of a 
good illuminating power; third, that the coal be as free 
as possible from sulphur; and fourth, that the coke fur- 
nished by the carbonization of the coal be bulky, and 
at the same time firm, that is, not inclined to be gran- 
ular. 



62 COMBUSTION OF COAL. 

"1. The percentage of the volatile matter in the 
coals usually employed in gas-making is from twenty- 
five to forty, and in cannel coal it rises to sixty or sev- 
enty per cent., a portion being nitrogen and oxygen. 
A ton of coal should produce from eight thousand to 
nine thousand feet of carbureted hydrogen or illuminat- 
ing gas, or from four to four and half feet per pound, the 
latter, as is well known, being the product of a fair aver- 
age sample of Youghiogheny coal. Gas works practi- 
cally obtain more gas per pound than the chemists in ana- 
lyzing the coal, doubtless through the re-distillation of 
tafry matter and its conversion into permanent gas. 
Besides this, at gas works the measurement is taken at 
a high temperature, a difference of five degrees chang- 
ing the volume of gas about one per cent. By using 
the steam-jet exhaust (a recent improvement) an 
increased quality of gas is obtained, which would other- 
wise pass off in little bubbles in the tar. 

" 2. That the gas produced from the coal be of good 
illuminating power is very important. The standard of 
gas in our large cities ranges from fourteen to sixteen 
candle power. The standard candle in testing gas is of 
spermaceti, burning at the rate of one hundred and 
twenty grains per hour, compared with a standard gas- 
burner containing Hve cubic feet per hour. When it is 
supposed to give fifteen times the amount of light fur- 
nished by such standard candle, the gas is said to have 
fifteen-candle power, or be fifteen-candle gas. But the 
standard of illuminating power can easily be raised by 
the addition of a few per cent, of some rich cannel or 



GAS COAL. 63 



oil shale, or some substance of the character of albertite 
or grahamite; for example, from a coal that produces 
by itself fifteen-candle gas, by the addition of ten per 
cent, of cannel the gas was raised to the standard of 
eighteen candles. Many coals which produce gas of a 
low illuminating standard, but in large quantities, and 
which coke well, are used as gas coals. 

" 3. It is important that the coal should contain but 
a small proportion of sulphur compound, *as it is then 
easily purified, requiring less lime, producing a better 
quality of gas, and the coal may be safely stored with- 
out danger from spontaneous combustion. Good gas 
coal should not require more than one bushel of lime 
to purify five or six thousand feet of gas. The sulphur 
in coal is sometimes in combination with iron ; in other 
cases it passes off in a volatile state, leaving but little in 
the coke. For gas-making this latter is a disadvantage, 
as the less sulphur entering the gases the better, since it 
must be removed by purification. For the blast fur- 
nace, on the contrary, the less sulphur remaining in the 
coke the better, since it is the sulphur in the coke 
which is injurious, and not that in the hydrocarbons, 
which pass off at the top of the furnace stack. In some 
cases, however, when the gas carries with it most of the 
sulphur, the gas may be so superior in illuminating 
power as to warrant its use, notwithstanding its 
increased cost of purification. 

" 4. A ton of good coal, used in the manufacture of 
gas, should produce thirty-five to forty bushels of coke, 
weighing thirty-five pounds to the bushel. The coke is 



64 COMBUSTION OF COAL. 

used for heating the retorts, and should burn up clean, 
with but little clinker. There should be a surplus of 
coke when a large amount of gas is manufactured, 
besides that used in the gas-house, and this is valuable 
to the gas manufacturer as a merchantable product, 
especially in localities where coal of a good quality for 
domestic and other purposes is expensive." 

Non-caking Coals have the property of burning free 
in the tire much the same as wood charcoal burns — that 
is, heat does not cause them to fuse or run together in 
the fire. Perhaps the representative non-caking bitum- 
inous coal is the block coal of the western states, and 
noticeably, that of Indiana. 

Block Coal — An analysis of this coal is given on page 
56 and may be described as laminated in structure, con- 
sisting of successive layers of coal easily separated into 
thin horizontal slices not unlike slate ; between these 
slices of coal is a layer of fibrous carbon resembling 
charcoal. In appearance it has a dull lusterless face on 
the line of separation, and glistening or resinous black 
when broken at right angles to its horizontal face. A 
peculiarity of this formation and that which gives it its 
name, is the presence of fractures occurring in the coal 
bed at right angles, or nearly so, and extending from top 
to bottom of the seam, enabling the miner to get it out 
in rectangular blocks as these lines of fracture indicate 
or permit. 

It is a very strong coal and will burn well under a 
heavy load without crushing. The blocks are very com- 



CARBONIZATION OF COAL. 65- 

pact and will endure rough handling and stocking with- 
out suffering material loss from abrasion. This, in a- 
commercial point of view, gives the block coal great 
value over and above its other good qualities as a fuel 
for smelting iron and generating steam. 

Free-burning coal means the same as a non-caking, 
coal. 

CARBONIZATION OF COAL. 

Coke is the residual product of the carbonization of 
bituminous coal. The only coke of any commercial 
value is that made from caking coals. When screen- 
ings and small particles, as well as ordinary small lumps 
of such coal, are heated sufficiently high and protected 
from the atmosphere (in a closed vessel, such as a retort 
used in gas-making, or, coke ovens, when manufactured 
on a large scale), the volatile portions of the coal are 
driven off, and a coherent mass of fixed carbon, con- 
taining usually five to ten per cent, of earthy matter, 
alone remain; this is called coke. 

An analysis of the coal from which the celebrated 
Connellsville coke is made is given on page 57. This 
coke is very hard, occurs in long pieces not unlike ordi- 
nary stove wood, is of a steel grey color, having a bright 
metallic luster. It is used largely in the western states 
for the melting of iron in cupola furnaces, etc., and is a 
most excellent fuel for such purposes, requiring, how- 
ever, a strong draft, judging by comparison, about the 
same as Lehigh anthracite coal ; it yields an intense 
heat, burns free under a strong blast, and will support a 
(6) 



66 COMBUSTION OF COAL. 

considerable weight of iron above it in the cupola with- 
out crushing. 

The coke remaining after the distillation of coal in 
retorts, for the purpose of obtaining an illuminating 
gas, is known as gas coke. This is not so hard, is more 
easily ignited, and burns with a draft less intense than 
the preceding coke. This is a favorite fuel for domestic 
use, and burns well in steam boiler furnaces, or in any 
place where it is not subjected to any considerable 
pressure. Its power of resistance seems to be weakened 
by the manner in which it is coked, and the practice of 
cooling the charges drawn from the retorts by turning a 
stream of water on the incandescent coke while in con- 
tact w T ith the atmosphere; but aside from this, the 
quality of coal selected for gas-making has much to 
do with it, the selection being made with reference to 
the quantity of gas it will yield rather than the quantity 
and quality of coke remaining after distillation. 

THE INFLUENCE OF TEMPERATURE AND PRESSURE IN THE YIELD OF 

COKE, 

Temperature — The quality of coke is affected by the 
temperature at which it is made. In no case can coking 
occur at a temperature less than that at which coal suf- 
fers decomposition. Coking is not a mere fusing of coal 
into a mass; it is rather a process of distillation, in which 
all the volatile portions of the coal are separated from 
that solid portion called iixed carbon. This distillation can 
only occur at a high temperature, and observation show r s 
that as a general rule the higher the temperature, and 



COKE. 



67 



the longer the exposure to that temperature, the harder, 
more dense, and less easily combustible will be the coke. 

M. de Marsilly (20) tried the effect of coking during 
ninety-six, and one hundred and twenty hours, and found 
that no advantage was derived by prolonging the pro- 
cess beyond forty-eight hours. 

Pressure — In order to test the effect of pressure on 
the quality of coke, experiments were made in the lab- 
oratory of Professor E. T. Cox, during which he was 
assisted by Dr. G-. M. Levette. The following table gives 
the results of the experiments as determined by them : 
Table X — Coals Coked uxder Different Degrees of Pressure. 





PLATINUM 


IRON RETORT. 


NO. 














PROXIMATE 


NO 


3 INCHES 


6 INCHES 


12 INCHES 




ANALYSIS. 


MERCURY. 


MERCURY. 


MERCURY. 


MERCURY. 


1 


52.40 


59.10 


62.00 


62.80 


59.40 


2 


52.50 


54.35 


54.00 


54.30 


56.50 


3 


55.50 


56.10 


56.40 


57.95 


56.15 


4 


57.50 


58.85 


60.40 


58.50 


59.25 


5 


58.50 


62.20 


61.75 


62.60 


63.40 


6 


57.90 


65.05 


65.00 


• 65.10 


66.10 



NAME OF THE MINE OR OWNER. 



No. 1. 

No. 2. 
No. 3. 
No. 4. 
No. 5. 
No. 6. 



H. K. Wilson's, Sullivan county, Indiana. 
Simpson's, Knox county, Indiana. 
Shepard & Haslett's, Knox county, Indiana. 
Woodruff & Fletcher's, Clay county, Indiana. 
Barnett's, Clay county, Indiana. 
Stone's, Pittsburg, Pennsylvania. 



68 COMBUSTION OF COAL. 

Eos. 1, 2, 3 and 6 of the table are caking coals; Nos. 
4 and 5 are non-caking or block coals. 

The coke from Xo. 1 made in the retort, without 
pressure, was moderately firm, close textured, of grayish 
black color and without luster; with a pressure exerted 
by a column of water four inches high (not given in 
the table) the coke was not increased in weight, but- 
appeared more compact and presented a radiated, crys- 
talline structure, the rays run from a small central core 
to the circumference. This peculiar structure was lost 
when the pressure was increased. Up to a six inch pres- 
sure of mercury there was a gain of 3.7 per cent, of 
coke, which was very dense and strong. At twelve 
inches of pressure the per cent, of coke was scarcely 
more than that obtained without pressure, and gave 
signs of puffing. From this it will be seen that six 
inches of mercury gives the maximum per cent, of coke, 
and that beyond this the heat is sufficient to liquify the 
fixed carbon, and expand its particles so as to make a 
puffed, porous cake. There was little difference in the 
time occupied in coking, with or without pressure. 
The average time was forty-five minutes. 

Instead of the coal being powdered, as was the case 
in the above experiment, some pieces a little larger than 
a pea were coked under six and twelve inches pressure, 
and they were found unchanged in shape except that 
the edges' were slightly fused, and they were cemented 
together like a pop-corn ball. The color and appear- 
ance of the pieces resembled anthracite coal far more 
than coke. Under twelve inches pressure the pieces 



COKE. 



69 



were slightly swollen, but in color and structure other- 
wise presented the same appearance as the former. 

Nos. 2 and 3, caking coals, gave a cellular coke with- 
out pressure, and the cells were only slightly enlarged 
by twelve inches of pressure. The weight of coke in 
No. 2, at twelve inches, was increased by four per cent., 
and that of No. 3 by only 0.65 per cent., while under 
six inches pressure the increase was 2.45 per cent. 

Though these coals do not puff up, under pressure, 
as much as Nos. 1 and 6, the result clearly points out 
that all three belong to a class of coals that will not 
make a good coke under pressure, but that the coking 
oven, like the retorts at the gas works, should be sub- 
jected to a process of exhaustion. 

No. 4 coked without pressure, and gave a coke that 
possessed but little cohesion ; as the pressure increased 
the coke was more compact, and under twelve inches 
pressure it was strong and good ; the color, like that of 
No. 1, resembled anthracite rather than coke; the great- 
est increase was produced by pressure of twelve inches, 
and only amounted to 1.75 per cent. 

No. 5. This is one of the dryest burning of the block 
coals and the particles were but slightly coherent even 
under a pressure of twelve inches ; the increase in weight 
at this pressure amounted to 4.9 per cent. 

The greatest pressure exerted on the block coals did 
not cause the carbon to become liquid as in the coking 
coals and the particles were simply cemented together 
by fusing on the surface. Lumps, when coked under 



70 COMBUSTION OF COAL. 

pressure, do not therefore swell, but ratlier become more 
dense and homogeneous with an increase of heat. 

No, 6. The effect of pressure on this coal was quite 
different from that of No. 1, and equally as remarkable. 
The weight of the coke continued to increase up to a 
pressure of twelve inches, where it gained 8.2 per cent, 
over the result in the first column, but it was puffed up 
until the shape resembled a hen's egg and contained a 
large cavity in the center of the mass. The fracture 
presented also a cellular structure like a sponge. "With- 
out any pressure this coal gave n moderately dense coke 
but continued to puff up with every inch of pressure 
added. 

It appears that, in order to make a homogeneous 
good coke, the fixed carbon of the coal must be of a kind 
that will melt at the lowest possible temperature, for if 
the process of coking produces the least pressure on the 
volatile hydrocarbons, whereby there is an increase of 
heat, such pressure causes so complete a liquefaction and 
expansion of the fixed carbon that the coke is left cellu- 
lar instead of being compact. If such a coal is coked 
by covering it with an inch of sand and leaving the cover 
of the retort oft', the coke will be dense and strong and 
without cells that are perceptible to the eye. On the 
other hand, coals, like the block coal of Indiana, which 
requires a very high temperature to meet its fixed car- 
bon, does not have its fixed coke expanded by heat 
induced by an over-pressure of the eliminated gas, but 
as far as tried in the above experiments, the solidity of 
the block coal coke increased as the pressure was aug- 



COKE. 71 



merited by raising the column of mercury through which 
the gas had to escape ; such coals then are eminently 
adapted, in the raw state, for smelting iron in the blast 
furnace. 

Mr. A. L. Steavenson read a paper before the Iron 
and Steel Institute, at Newcastle, England, on the man- 
ufacture of coke, in which he gives some interesting- 
data in regard to coking coal. After giving a descrip- 
tion of the furnaces employed in the particular manu- 
factories to which he refers in the first part of his paper, 
he then goes on to say : "Two hundred and thirty tons 
of coal of the following approximate composition, 

TONS. 

Oxygen 15.3 

Carbon 195.3 

Hydrogen 10.4 

Nitrogen 2.3 

Sulphur 1.4 

Ash 5.3 

230.0 
Yield, on coking, about sixty per cent, of coke, of the 
following approximate composition : 

TONS. 

Carbon 132.7 

Ash 5.3 

138.0 
"Therefore, the composition and weight of the mate- 
rials lost in coking are, 

TONS. 

Carbon 62.6 

Hydrogen 10.3 

Nitrogen 2.3 



(Z COMBUSTION OF COAL. 

Sulphur 1.4 

Oxygen 15.3 

To complete the combustion of these into N, C0 2 II 2 
unci S0 2 are required 1023.4 tons of air, making a total 
weight of waste gases of 1115.4 tons, of which : 

790.3 tons are nitrogen. 
229.5 tons are carbonic acid. 
92.8 tons are steam. 
2.8 tons are sulphurous acid. 

Which, at a temperature of fifteen hundred deg. Fahr., 
will occupy a space of one hundred and twenty-three 
million nine hundred and ninety-nine thousand cubic 
feet; and since the coking of two hundred and thirty 
tons of coal occupies, on an average, eighty-four hours, 
we have twenty-four thousand four hundred and ninety- 
three cubic feet per minute, or four thousand and five* 
cubic feet less than the observed quantity as above. 

"Next, as to the heat commonly wasted. We have 
1115.4 tons of mixed gases, at a temperature of fifteen 
hundred deg. Fahr., which, if they could be reduced to 
the temperature of the atmosphere (say sixty deg. 
Fahr.), we would have the following heating value in 
tons of II, (water) raised one deg. Fahr. 

TEMPERATURE. 

TONS. DEGS. SP. HEAT. TONS H2 O. 

N 790.3 X 1440 X .244 = 277,680 

CO, 229.5 X 1440 X -210 == 71,384 

H, 92.8 X 1440 X -475 = 63,477 

S0 2 2.8 X 1440 X -1 ; >"> = 625 

Tons H 2 O (water) 413,166 

* This four thousand and five cubic feet refers to some experiments at the 
kilns. B. 



CANNEL COAL. 73 



"Which is equivalent to evaporating 415 tons of water 
at 212° Fahr. But owing to the fact that the tempera- 
ture of the gases was only reduced 750° Fahr., instead 
of 1,440° Fahr., the above quantity is reduced to about 
one-half, or 216.1 tons, evaporated in eighty-four hours, 
or 2.6 tons in one hour. This was tested in an actual 
experiment (on the two boilers supplied with the gases 
from fifty ovens, coking the 230 tons in eighty-four 
hours), the quantity evaporated in one hour being 2.4 
tons, an approximation quite as close as can be expected. 
"The total theoretical heat actually developed in the 
process of coking at the above rate is equivalent to 
evaporating 17 tons of water per hour, which is thus 
expended : 

TONS. 

Heat utilized by the boilers 2.40 

Heat escaping in chimney 2.54 

Heat lost in radiation from ovens and flues 12.06 

17.00 

"Thus, even in the plan described, but a small per- 
centage of the total heat generated in the ovens is util- 
ized, although if this was carried out throughout the 
district of South Durham, where in colliery boilers not 
more than 6 lbs. of water, on the average, is evaporated 
per 1 lb. of coals, we should have a saving of 1,085,869 
tons of coal per annum, or a money value of £271,467 
(81,313,900.28)." 

CANNEL COAL. 

Cannel Coal is a variety of bituminous coal very rich 
in hydrogen. From the amount of combustible matter 
which it contains, and the readiness with which this is 



74 COMBUSTION OF COAL. 

given off in combustion, accounts for the name given it 
by the miners as cannel, a corruption of candle coal. 
This coal kindles readily, and burns without melting, 
emitting a bright flame like that of a candle. When 
thrown in the fire the piece splits up into fragments, 
producing a crackling noise which, from a fancied 
resemblance, has also received the name of parrot coal. 
In appearance this coal differs from all other bitu- 
minous coals; its structure is more nearly homogeneous 
than others, being a compact mass, varying from brown 
to black in color, and having usually a dull resinous 
luster. When broken it does not usually preserve any 
distinct order of fracture, and is liable to split in any 
direction. On account of its being excessively rich in 
hydro-carbons it is highly esteemed as a gas-coal, pref- 
erence being given to those coals in which hydrogen 
bears the greatest proportion to the contained oxygen. 

ANALYSIS OF VARIOUS CANNEL COALS. 

An analysis of cannel coal from near Franklin, Pa., 
by Professor W. P. Johnson, gave, 

PEE CENT. 

Fixed Carbon 40.13 

Volatile matter 44.85 

Earthy matter 15.02 

100.00 
Cannel coal from Dorton's Branch, Cumberland 
river, Ky. Coal : close-textured, concentric-structured, 
brilliant, conchoidal. By Dr. D. P. Owen. 

PEE CENT. 

Fixed carbon 55.1 

Volatile matter 42.0 



CANNEL COAL. 75 



Earthy matter 2 

100.0 
Specific gravity, 1.25. 
Ashes, orange-colored. 

Breckenridge, Ky., cannel coal. Proximate analysis 
by Dr. Peters. 

PER CENT. 

Carbon 32.00 

Volatile matter 54.40 

Moisture 1.30 

Ash 12.30 

100.00 
This coal, by elementary analysis, gave, 

PER CENT. 

Carbon 68.128 

Hydrogen 6.489 

Nitrogen 2.274 

Oxygen and loss 5.833 

Sulphur 2.476 

Ash 14.800 

100.000 
Buckeye Cannel Coal Company, Davis county, 
Indiana. By Professor E. T. Cox. 

PROXIMATE ANALYSIS 

PER CENT. 

Fixed carbon 42.00 

Gas 48.50 

Hydroscopic water 3.50 

Ash, white 6.00 

100.00 
Coke — is laminated, not swollen, lusterless. 
Specific gravity, 1.229. 
One cubic foot weighs 76.87 lbs. 



76 COMBUSTION OF COAL. 



ULTIMATE ANALYSIS OF THE SAME. 

PER CENT. 

Carbon 71.10 

Hydrogen 6.06 

Oxygen , 12.74 

Nitrogen 1.45 

Sulphur 1.00 

Ash 7.65 

100.00 
The heat units in this coal are thirteen thousand one 
hundred and thirty-one, thus : 

.7110 carbon X 14,544= 10,340 carbon heat units. 
.045 available hydrogen X 62,032 =2,791 hydrogen heat units. 
10,340 carbon heat units. 
2,791 hydrogen heat units. 

13,131 total heat units in the coal. 
SEMI-BITUMINOUS COAL. 

Semi-bituminous Goal is not so hard, and contains 
more volatile matter than true anthracite. In this, as 
in all other classification of coals, its limits must be 
somewhat arbitrarily fixed. In appearance it more 
closely resembles the anthracite than the bituminous 
coals, differing from the former: in fracture, as being 
less conchoidal; it is not so hard; is of a less specific 
gravity; and when thrown upon the fire it kindles 
much more readily and burns faster than anthracite. 
It takes high rank as a fuel ; although, containing less 
carbon than anthracite, it is quite as desirable on 
account of the readiness with which it kindles, and the 
quantity of heat it is capable of giving off when burned 



SEMI- ANTHRACITE COAL. 77 

in steam boiler furnaces, and in stoves for domestic use. 
It is much more easily regulated in burning than anthra- 
cite, and is almost entirely free from the smoke and soot 
of ordinary bituminous coal. 

Analysis of semi-bituminous coal from Cumberland ', 
Maryland. By Professor "W. R. Johnson. 

Specific gravity, 1.41. 

PER CENT. 

Fixed carbon 68.44 

Volatile matter. 17. 28 

Earthy matter 13.98 

Sulphur 71 



100.41 

Blossburg, Pennsylvania, from Geological Survey of 
Pennsylvania. 

Specific gravity, 1.32. 

PER CENT. 

Fixed carbon 73. 1 1 

Volatile matter 15.27 

Earthy matter 10.77 

Sulphur 85 



100.00 
The heat units in this coal determined as below are 
thirteen thousand one hundred and fifty-five: 

Carbon 7311X14,544 = 10,633 

Volatile matter 1527X20,115= 3,072 

Less 1527X 3,600=- 550 2,522 



Total heat units 13,155 

SEMI-ANTHRACITE COAL. 

The semi-anthracite coals are restricted, with few 
exceptions, to those coals which possess on an average 



78 COMBUSTION OF COAL. 

from seven to eight per cent, of volatile combustible 
matter. In consequence of this element, part of which, 
at least, resides probably in a free or gaseous state in 
the cells or clefts of the coal, this variety kindles more 
promptly, and, when sufficiently supplied with air, burns 
more rapidly than the hard anthracite. 

Wilkesbarre, Pennsylvania, semi-anthracite, de- 
scribed as compact, conchoidal, iron-black, splendant. 
Geological suiwey of Pennsylvania. 

Specific gravity, 1.40. 

PER CENT. 

Fixed carbon 88.90 

Volatile matter 7.68 

Earthy matter , . , 3.49 



100.07 

Neglecting the .07 we have in this coal 14,199 units 

of heat, thus — 

Carbon .8890x14,544= 12,930 

Volatile matter 0768X20,115= 1,545 

Less 0768X 3,600-= 276 1,269 



14,199 

ANTHRACITE COAL. 

True anthracite, when pure, is slow to ignite, con- 
ducts heat very badly, burns at a very high tempera- 
ture, radiates an intense warmth, and is difficult to 
quench. Generating almost no water during its com- 
bustion, it powerfully dessicates the atmosphere of an 
apartment in which it is burning. 

It consists, when pure, (23) of 

Carbon from 90 to 94 per cent 

Hydrogen..... from 1 to 3 per cent. 



ANTHRACITE COAL. 






79 



Oxygen and nitrogen from 1 to 3 per cent. 

Water from 1 to 2 per cent. 

Ashes from 3 to 4 per cent. 

The constituents which vary most are, of course, the 
carbon and earthy matter. 

Hard anthracite, from its great richness in carbon 
and its density, stands at the head of all coals for its heat 
generating power, if adequately supplied with air. It is 
the most economic of all fuels — weight for weight — for 
smelting and melting iron and the other metals. 

The superior density of hard anthracite over every 
other kind of coal, by lessening the room demanded for 
stowage, gives it a decided preference in this respect as 
a fuel for ocean steamers. 

In burning it neither softens nor swells, and does not 



give off smoke ; the flame is quite short, and has a yel- 
lowish tinge when first thrown upon the fire, which 
soon changes to a faint blue, with occasionally a red 
tinge. The flame being quite short and free from parti- 
cles of solid carbon, has the appearance of being trans- 
parent. 

When broken it presents a conchoidal appearance, 
and appears quite homogeneous in structure. It will 
stand weathering and stowage better than other coals. 

Analysis of Anthracite Coal from Tamaqua, Pennsylvania. 

GEOLOGICAL SURVEY OF PENNSYLVANIA. 

This coal is described as compact, slaty, con- 
choidal, greyish black, splendant. 



80 



COMBUSTION OF COAL. 



Specific gravity, 1.57. 
Fixed carbon 




PKR CENT. 

92.07 


Volatile matter 




5.03 


Earthy matter 


ad of coal 


2.90 


Ashes, white. 

Units of heat in 1 doui 


100.00 
14.221 



Beaver Meadow (Pa.) Anthracite. Prof. W. R. 
Johnson. 

Specific gravity, 1.55 

PEE CENT. 

Fixed carbon 90.20 

Volatile matter 2.52 

Earthy matter 6.13 

98.85 
ISTo explanation is given by Professor Johnson for 
the 1.15 per cent, loss not accounted for in the analysis, 
but neglecting this, we have 13,535 units as the calorific 
power of this coal, determined as follows: 

Carbon 9020X14,544 = 13,119 

Volatile matter 0252X20,115 = 507 

Less 0252X3600 = 91= 416 



Total heat units 13,535 



CHATTER IV. 

ANALYSIS OF COAL. 

Analysis, Chemical, Qualitative, Quantitative, Proximate — Selection- 
of Samples for Analysis — Method of Conducting a Proximate 
Analysis — Elementary Analysis — Determination of Sulphur 
and Phosphorus — Carbon — Hydrogen — Carbureted Hydrogen 
— Sulphur — Products obtained from Coal. 

Analysis — The separation of a body into its constitu- 
ent elements is called chemical analysis; when it is- 
desired to know simply what elements compose a body 
it is known as qualitative analysis: when the quantity of 
each element is to be determined it is then known as 
quantitative analysis. When, as in the ordinary analysis 
of coal, it is desirable to determine what percentage of 
volatile matter, fixed carbon, and ash, are contained in 
a given sample, this process is known as proximate anal- 
ysis, and simply informs as to the physical peculiarities 
of the coal and not as to its elementary composition. 

The elementary analysis of coal shows it to be prin- 
cipally composed of the following simple substances: 

Carbon : Oxygen ; 

Hydrogen; Sulphur; and 

Nitrogen; Ash. 

Ash is not a simple substance, but represents the 
incombustible matter of whatever composition remain- 
ing in the furnace after combustion. 

By proximate analysis the coal would be said to 
contain 
(?) 



82 COMBUSTION OF COAL. 

Fixed carbon; Moisture or water; 

Volatile matter ; Ash. 

In the analysis of coal it is desirable to know, 

1. The percentage of volatile matter it contains. 

2. The percentage of fixed carbon. 

3. The percentage of earthy matter, or the presence 
of such bodies as do not contribute to its heating value. 

This can only be arrived at by a process of destruc- 
tive distillation. 

Professor E. T. Cox, State Geologist of Indiana, has 
given the analysis of coals particular attention. His 
suggestions in regard to samples, and his method of 
conducting analysis, whether proximate or elementary, 
are given below; also, his method of determining the 
amount of sulphur, phosphorus, iron and alumina in 
coal. 

Samples — It is a matter of no little difficulty to select 
from a mine a proper sample for analysis, at least such 
a sample as will represent the average commercial value 
of the seam. The best way, therefore, is to take a 
sample from the top, middle and bottom of the seam. 
These should be carefully labeled, wrapped in paper and 
sent to the laboratory as soon thereafter as practicable. 
On arriving at the laboratory they should be taken in 
hand at once. About a pound of each sample should 
be pulverized fine enough to be passed through a porce- 
lain colander with one-tenth inch perforations; then 
transferred to bottles with good cork stoppers. Each 
bottle should be labeled, showing the date of mining, 
when bottled, name of mine, etc. These bottles serve 



PROXIMATE ANALYSIS. 



as stocks from which the different quantities are to 
be taken that serve for analysis. It is not a good 
plan to mix the portions taken from different parts of 
the seam and consider the mixture an average sample, 
so that one set of analysis may serve ; for though it 
might furnish a fair statement of the commercial value 
of the seam, it would leave us in ignorance of much use- 
ful information in regard to the true character of the 
seam. 

PROXIMATE ANALYSIS. 

One gram is charred in a covered platinum crucible 
of about one fluid ounce capacity. The heat is derived 
from a three-jet Bunsen gas burner, and the crucible kept 
at a bright red heat until the escaping gas ceases to burn 
and the condensed carbon disappears from the cover 
The weight of the charred mass gives the coke, and the 
volatile matter is estimated by the loss. To determine 
the hygroscopic water, one decigram of pulverized coal 
is weighed in a small, shallow platinum capsule and 
placed in a hot-air bath, where it remains at a tempera- 
ture of 100 to 105 deg. Cent, for one hour; the loss gives 
the water. The capsule, with the dry coal, is then 
placed over a strong flame of a Bunsen burner until 
it is consumed to ash. 

The weight of the ash is deducted from the coke to 
find the fixed carbon, and the weight of the water is 
deducted from the volatile matter to find the per cent, 
of combustible gas. 

All this appears very simple, but it requires great 
care and attention to obtain reliable results. The tern- 



84 COMBUSTION OF COAL. 

perature of 100° C (212 Fahr.) is recommended, 
since it is believed that a higher temperature is no 
more effective and is more liable to produce decompo- 
sition of the volatile constituents. 

ELEMENTARY ANALYSIS. 

The combustion is best performed in a hard glass 
tube, twenty inches long and three-quarters of an inch 
in diameter. 

Twelve inches of the posterior end is filled with a 
tightly-rolled coil of fine copper gauze. This is oxidized 
by drawing air through the red-hot tube with an aspi- 
rator. The usual appliances are used to dry the oxygen 
and free it from carbonic acid and other impurities, 
and also arrest the hydrogen, sulphur and carbonic acid. 

Previous to commencing the combustion, a current 
of pure oxygen is passed through the heated tube to 
complete the oxidation of the copper and expel the last 
trace of moisture. Two decigrams of pulverized coal 
are now placed in a platinum boat and inserted in the 
anterior part of the tube, about three inches from the 
copper. The heat of the gas furnace is applied with 
due precaution, and the combustion is completed when 
the coal has been burnt to ash and oxygen bubbles pass 
freely through the potash apparatus. When the hydro- 
gen, sulphur, potash apparatus and potash U tube have 
been weighed, another analysis may be proceeded with, 
and in this way as many as four combustions may be 
made in a day. A good tube will serve for ten or 
twenty combustions. The potash apparatus should be 



ELEMENTARY ANALYSIS. 85 

renewed after every third combustion, in order to insure 
a proper absorption of the carbonic acid. 

The advantages to be derived from this mode of 
conducting the analysis, are : You are enabled to watch 
the combustion of the coal and see when it is com- 
pleted; the ash may be determined at the same time 
and the tube is at once ready for the reception of 
another sample of coal. Nitrogen is determined by 
Varrentrapp and Will's method, L e., by conversion into 
ammonia. The ammonia is received in a measured 
quantity of standard oxalic acid, and the amount of 
free acid remaining is determined by neutralizing with 
a standard solution of soda. The quantity of acid sat- 
urated by ammonia is then found from the difference. 

DETERMINATION OF SULPHUR AND PHOSPHORUS. 

There is, generally speaking, less reliance to be 
placed in published statements of the amount of sul- 
phur and phosphorus in coals than in any one of its 
other elementary constituents. 

The results are, as is w^ell known, generally under 
rather than over the actual amount of sulphur present 
in coal. 

The loss is due to a portion of the sulphur being 
converted into sulphureted hydrogen and the phos- 
phorus into phosphureted hydrogen, which escapes 
during the process of dissolving the coal. In order to 
avoid this loss, five decigrams of coal are fused with 
eight grains of caustic potash and two grains nitrate of 
potash, in a silver crucible. 



86 COMBUSTION OF COAL. 

Both the caustic potash and nitrate of potash should 
be tested for sulphur and the per cent, marked upon the 
bottle. The half gram of powdered coal is placed in 
the crucible and moistened with alcohol, eight grams of 
potash are then put in with the coal and placed over a 
moderate heat until the potash is melted, after which 
two grams nitrate of potash are added, the whole is 
kept at a gentle heat for about two hours or until all the 
moisture is expelled; the heat is then increased until 
all ebullition ceases. The coal should dissolve without 
deflagration from ignition. After cooling, the contents 
of the crucible are dissolved out with water and neutral- 
ized with hydrochloric acid, evaporated to dryness, mois- 
tened with hydrochloric acid and re-dissolved with 
water. Filter out the silicic acid, heat the filtrate and 
precipitate the iron and alumina with ammonia and 
determine the sulphuric acid in the filtrate with chloride 
of barium. 

The phosphoric acid is precipitated with the iron, 
and to separate it, the precipitate is dissolved from the 
filter with a weak solution of hydrochloric acid, and 
then evaporated to dryness to separate the last trace of 
silicic acid. 

Moisten with nitric acid, dissolve in water, filter and 
precipitate the phosphoric acid with molybdate of 
ammonia. Wash the precipitate as directed by Fre- 
senius, dissolve with ammonia and precipitate phosphoric 
acid with sulphate of magnesia. In order to determine 
the per cent, of iron and alumina, it is better to take 
another half gram of coal and fuse as before. The iron 



CARBON. 



87 



and alumina are then precipitated from the hot solution 
with ammonia, and the alumina is separated by digest- 
ing the precipitate with hydrate of potash in a silver 
crucible. 

This mode of determining the sulphur, phosphorus, 
iron and alumina in coal, is simple, expeditious and accu- 
rate. It has been adopted after repeated trials of all 
other known processes, and leaves nothing to be 
desired. 

CARBON AND HYDROGEN. 

Carbon — (Symbol C; atomic weight 12). This is one 
of the most widely diffused and abundant of the ele- 
ments. It exists in several allotropic states; that is, it 
exists in several conditions, each having different physi- 
cal properties, whilst its chemical properties remain 
unchanged. 

The commonest forms in which pure carbon occurs 
are the diamond, black lead and charcoal. We can 
scarcely imagine three solids more unlike in their phys- 
ical properties than these, yet chemically, they are the 
same thing; that is, they yield upon analysis nothing 
but carbon. It is the principal constituent of anthra- 
cite coal; it constitutes about one-half of bituminous 
coal; and is an essential element in organic bodies, from 
which it may be separated in the form of charcoal, by 
distilling off the more volatile elements. 

Carbon unites directly with oxygen, sulphur, nitro- 
gen, and a few of the metals, the latter at high temper- 
atures only. The two direct inorganic compounds of 
carbon and oxv^en are known as carbonic oxide and 



88 



COMBUSTION OF COAL. 



carbonic acid; the proportions are shown in the follow- 
ing table: 



Table XI. 





SYMBOL. 


COMPOSITION. 




BY WEIGHT. 


PERCENTAGE. 




CARBON. 


OXYGEN. 


TOTAL. 


CARBON. 


OXYGEN. 


TOTAL. 


Carbonic Oxide- 
Carbonic Acid.... 


C 

co 2 


12 
12 


16 


28 
44 


42.86 
27.27 


57.14 
72.73 


100 
100 



These are the two principal gases formed in the fur- 
nace by the combustion of the carbonaceous portions of 
the fuel. The table of products obtained from coal 
(page 94) show about fifty different combinations of 
carbon with different elements and in different propor- 
tions. 

Almost all the elementary substances of which the 
specific heat and atomic weight are known, give, when 
these two properties are multiplied into each other, a 
product approximating an average of 6.34. Carbon is 
one of the exceptions to this rule, as the following will 
show : 



SPECIFIC ATOMIC 

HEAT. WEIGHT. PRODUCTS. 

12 



Carbon (diamond) 0.1469 12 1.76 

Carbon (graphite) 0.2008 12 2.41 

Carbon (wood charcoal) 0.2415 12 2.90 

The other two exceptions are boron and silicon. 
Carbon is quite remarkable for the differences in its 
physical conditions, and this is sometimes brought for- 
ward as a partial reason for the low product shown in 



HYDROGEN. 89 



the above table. There is no doubt this fact has much 
to do with it, but is not a very satisfactory way of dis- 
posing of so marked a difference in an element so 
widely diffused, and so generally employed in manufac- 
tures and domestic use. 

Hydrogen — (symbol H; atomic weight 1), is the light- 
est substance known. When pure it is colorless, taste- 
less, and inodorous. It is one of the few substances 
known to us only in the gaseous state. The theory that 
hydrogen is the vapor of a metal was proposed by the 
French chemist, Dumas, about forty-nine years ago 
(1830?), but from our knowledge of the gas we can 
scarcely imagine it to be solidified except by the with- 
drawal of heat until no more can be extracted, or, until 
absolute zero (461 deg. below the zero of Fahr.) is 
reached, when, of course, hydrogen would cease to exist 
as a gas, and would become inert or assume a solid state, 
and Would so remain until a rise in temperature would 
permit molecular motion, and so restore it to its gaseous 
form. Man} T experiments have been made to reduce it, 
if possible, to a liquid state. In the Scientific American, 
February 23, 1878, is an engraving of the apparatus 
employed by M. Cailletet, of Paris, in his experiments, 
during which he succeeded in liquefying hydrogen. It 
is said that M. Paoul Pictet has not only succeeded in 
obtaining liquefied hydrogen, but also solidified it at 
Geneva, January 10, 1878. 

Hydrogen is not found in a free state, though it is 
an essential element in all organic substances, from 
which it may be separated by a process of destructive 



90 COMBUSTION OF COAL. 

distillation. It occurs in nature in combination with 
carbon; the compound which contains it in greatest 
abundance is marsh-gas, of which hydrogen forms one- 
fourth, the formula being CH 4. This same gas often 
occurs in mines, where it is known as fire-damp. 

Under ordinary temperatures and at ordinary press- 
ures hydrogen has no tendency to enter into combina- 
tion with other substances. It combines with eight 
parts of oxygen to form water, but this combination 
does not take place spontaneously. The two gases will 
remain together as a mere mechanical mixture any 
length of time ; upon the application of a spark, how- 
ever, the chemical union of the two gases is instanta- 
neous and violent. Liquid water contains 1238 times its 
volume of free gaseous hydrogen, and when we con- 
sider the oceans of water throughout the world and 
the volume of hydrogen required to form this water, it 
makes a quantity which, expressed by ordinary meas- 
urements, is almost beyond comprehension. 

Pure hydrogen burns in the atmosphere with a pale 
blue light, scarcely perceptible in full daylight, giving 
off an intense heat. Favre and Silberman ascertained 
the heat of one pound of hydrogen burned in oxygen to 
be sufficient to raise the temperature of 62,032 pounds 
of water one degree Fahr. This is not equalled by any 
other known substance. 

Carbureted hydrogen has long been employed as an 
illuminating agent, and has been obtained by the distil- 
lation of the volatile portions of bituminous coal, yield- 



HYDROGEN. 91 



ing a hydro-carbon gas of the following approximate 
composition : 

Hydrogen 41.85 

Marsh-gas 39.] 1 

Carbonic oxide 5.86 

defines 7.95 

Nitrogen 5.01 

Carbonic acid 22 

100.00 

This composition will vary, of course, in different 
sections of the country, owing to different coals employed, 
and care in manufacture. The production of hydro- 
carbon gases on a large scale for illuminating purposes 
has engaged the minds of inventors not only, but has 
profitably employed vast sums of money in this great 
and almost indispensable industry. Within a few years 
past the possibility of economically decomposing water 
in order to utilize its hydrogen as an illuminating agent 
has been fully demonstrated on a large scale, and it 
appears as if, in addition to its employment as an illu- 
minating agent, it, at no very distant day, by virtue of 
its extraordinary and unparalleled heating power, is des- 
tined to supercede our present wasteful method of 
heating city homes, mercantile and manufacturing build- 
ings, etc., promising at once a heat in any desired quan- 
tity, easily controlled, with perfect cleanliness, and 
more economical in many cases than crude fuel. 

Hydrogen unites with nitrogen to form ammonia, 
the formula being NH 3 . 



92 COMBUSTION OF COAL. 

Sulphur — [symbol S; atomic weight 32), is often 
found in coal in combination with iron, and is known 
as iron pyrites. Some specimens are of great beauty, 
but underneath this attractive exterior lurks a danger- 
ous enemy to steam boilers. Sulphur is highly inflam- 
mable, and when heated in the air to a temperature of 
about 482° Fahr. it takes fire and burns with a clear blue, 
feebly luminous flame, being converted into sulphurous 
oxide, S0 2 . In its chemical relations sulphur is the rep- 
resentative of oxygen, to which it is equivalent, atom to 
atom. Oxygen gas and sulphur vapor alike support 
the combustion of hydrogen, charcoal, phosphorus, and 
the metals to form precisely analogous compounds. 

"The presence of sulphur in common coal gas has 
received considerable attention, from a sanitary point of 
view, by gas chemists, who are somewhat divided in 
their opinions as to the precise state in which sulphur 
is introduced into the air. Mr. Thomas Wills, F. C. S., 
in a lecture delivered before the British Association of 
Gas Managers (1878), gives as his opinion that "The 
sulphur is first of all burnt to sulphurous acid, that 
then a certain portion of this sulphurous acid is oxid- 
ized into sulphuric acid, and that the amount so oxid- 
ized depends upon circumstances; but that given a suf- 
ficient length of time, the whole of the sulphurous acid 
will be oxidized into sulphuric acid. E"ow as to the 
circumstances: If the sulphurous acid is kept hot in 
the presence of moisture, then oxidization goes on more 
rapidly; if it be cooled down almost immediately after 
it is formed, the action is very slow, and within any 



SULPHUR. 93 



reasonable time it will be found impossible to entirely 
oxidize the whole of the sulphurous acid into sulphuric 
acid. Then, secondly, if the sulphurous acid meets 
with a base or with an easily-oxidizable substance with 
which, it can unite, it undergoes oxidation much more 
readily than if it remains in a state of free acid. 

"From my own experiments, I believe that under 
ordinary circumstances, considerably less than one-half 
of the sulphurous acid produced by the combustion of 
coal gas is oxidized in any reasonable time into sulphuric 
acid, and in this I am supported by several gentlemen, 
who not being connected with the coal gas industry, are, 
nevertheless, thoroughly acquainted with the behavior 
of sulphurous acid when used in the manufacture of 
alkali." 

Mr. Wills also makes the startling statement, in the 
same lecture, that if we regard the amount of coal burnt 
in London as eight million tons per annum, and we take 
that coal to contain one per cent, of sulphur which is 
burnt — whether in the form in which it is sent into the 
houses in gas, or in furnaces, or in grates, it is burnt in 
some way — and which is a low average, we shall have 
eighty thousand tons of sulphur thrown into the air in 
the form of sulphurous acid, and if that is calculated 
into oil of vitriol, it will amount, in one year, to two 
hundred and forty thousand tons of oil of vitriol sent 
into the atmosphere of London alone by the combustion 
of coal. 

Though the amount of sulphur in the aggregate 
appears very large from the figures in the above para- 



94 



COMBUSTION OF COAL. 



graph, it is not too large for the atmosphere to fully take 
care of it without detriment to health or comfort, but 
what concerns us chiefly in our present line of inquiry 
is, the effect of sulphur in coal upon steam boilers. The 
corrosive action of sulphur compounds on iron will be 
found in Chapter VIII. 



PKODUCTS OBTAINED FROM COAL. 

BY HENRY A. MOTT, Jr. 

(Benzole 



Coal. 



Gas, illum- 
inating, etc. 

Tar 

Ammonia.... 

Water 

Coke for 
fuel 



Oils, 30 
per 



30 | 
ct. J 



}( 



Used to 

Benzole iSSZifr make 

Naphtha -{ *■ J \ Aniline. 

Naphtha Used for Varnishes. 

Xylole Used for Small-pox. 

FURNISHES 

f Carbolic Acid ") f Used for Disin- 
Cresylic Acid, j ~) fectants. 

Dead Oil -I Naphthalene Dyes, etc. 

Anthracene, % per ct.) Used to make 

Chrysene ) Alizarine. 

Pitch, 70 )f Used for Roofing and Pavements, 
per ct. j 1 Anthracene, 2 per cent. 



The preparation of alizarine from anthracene : 

Potassic 
Acetic Acid. bichromate. Anthraquinone. 



Anthracene. 



Cw Hio + C2 Hi O2 + K 2 Crc Ot = Gu H O2 + etc. 

Anthraquinone. Bromine. Dibromoanthraquinone. 



Cm Hs O2 + 2 Br = Cm He Br2 O2 + etc. 
Dibromoanthraquinone. Potassic hydrate. Alizarine. 



Cm He Bra O2 + 2 KHO = Cm H 8 Ot + etc. 

The following table gives a list of the products ob- 
tained by the distillation of -eoal : 



PRODUCTS OBTAINED FROM COAL. 



95 



NAME. 


FORMULA. 


GAS OR VAPOR. 
SPECIFIC GRAVITY. 


BOILING POINT. 

DEGREES. 

CENTIGRADE. 


Atmospheric air 




1.000 




Hydrogen 


H 


0.069 




Nitrogen 


N 



0.971 
1.106 




Oxygen 




Ammonia 


N Ha 


0.590 


33 


Aqueous vapor 


H2O 


0.622 


100 


Carbonic oxide 


CO 
C O2 


0.967 
1.529 




Carbonic anhydride 


109 (Fahr.) 


Cyanogen 


CN 


1.801 




Sulphurous anhydride. 


SO2 


2.2112 


+13.09 (Fahr.) 


Carbon disulphide 


CS2 


2.645 


47 


MARSH GAS SERIES. 








Methyl hydride 


CH* 


0.5596 




Ethyl hydride 


C2H6 


1.037 






CsHs 


1.522 




Butyl hydride 


C4H10 


2.005 


9 




C5H12 


2.489 


30 


Hexjd hydride 


CeHw 


0.669 


65 


Octyl hydride 


CsHis 


0.726 


108 


Decyl hydride 


C10H22 




158 


OLEFIANT GAS SERIES. 








Methylene 


CH2 
C2H4 


0.484 

0.9784 


39 


Ethylene, (defiant gas) 




Propylene (tritylene)... 


CaHe 


1.452 


—17.8 


Butylene 


C^Hs 


1.936 


+35 


Amylene 


CsHio 


2.419 


55 


Caproylene (hexylene) 


C6H12 


2.97 


61.3 


(Enanthvlene 


CtHh 


3.320 


99 



96 



COMBUSTION OF COAL. 



NAME. 


FORMULA. 


GAS OR VAPOR. 
SPECIFIC GRAVITY. 


BOILING POINT. 

DEGREES. 

CENTIGRADE. 


ACIDS. 








Hydrosulphocyanic 


H(CN)S 




85 


Ilvdrosulphuric 


H 2 S 


1.175 




Carbolic (phenol) 


H (Cells) 


1.065 (solid). * 


188 


Eosolic 


C20H6O3 






Brunolic 




0.7058 




Hydrocyanic 


HCN 


26.5 


Acetic 


C2H4O2 


2.079 


120 


ALCOHOLS. 




Cresylic alcohol 


CtHsO 




203 


Phlorylic alcohol, 


C«HioO 






BENZOLE SERIES. 








Benzole 


C 6 He 


2.695 


82 


Toluole 


CtH 8 
OsHio 


3.179 
3.179 


111 


Xylole 


129 


Cumole 


C 9 Hi2 
CioIIh 
CioIIs 


4.147 
4.632 
4.423 


148 


Cvmole 


175 


Naphthalene 


21 * 7 


Anthracene 


CuII'o 
Cell* 


6.741 


Melts at 213 


Chrysene 




Py rene 


C15II4 










Sp.Gr.Il20=] 


. 


Aniline 


H,(C t! H 5 )N 

(C (; A 5 )N 
(C 6 H 7 )N 


1 020 


182 


Pyridine 




115 


Picoline 


.09613 


134 


Lutidine 


(CtH 9 )N 

(ObHu)N 

(C 8 Hi3)N 

(CioHi 5 )N 

(CiiHw)N 


.921 


154 


Collidine 




170 


Parvoline 




188 


i 'oiidine 


211 


Rudidine 




230 



PRODUCTS OBTAINED FROM COAL. 



NAME. 


FORMULA. 


GAS OR VAPOR. 
SPECIFIC GRAVITY. 


BOILING POINT. 

DEGREES. 

CENTIGRADE. 


Viridine 


(Ci2H 9 )N 

(C9Ht)N 
(Cl0ll9)N 

(CnHn)N 
(CJl5)N 


1.017 


251 


Lecoline 


235 


Lepidin e 


260 


Crvptidine 


256 


Pyrrol 


133 







(8) 



CHAPTER V. 

COMBUSTION. 

Chemical Attraction — Muriate of Zinc — Gunpowder — Physical 
Changes — Chemical Changes — Definite Proportions — Multiple 
Proportions — Carbonic Acid — Carbonic Oxide — Law of Equiv- 
alents — Energy of Chemical Separation — Nature of Combus- 
tion — Conditions Necessary to Combustion — Luminosity — Igni- 
tion — Flame — Eecent Studies of Luminous Flames — Rate of 
Combustion — Temperature of Fire — Weight and Specific Heat 
of the Products of Combustion — Available Heat of Combustion 
— Efficiency of a Furnace. 

Combustion — This term is given to those chemical 
combinations in which there is a rapid union of an ele- 
ment such as carbon, or hydrogen, with another element 
— for which it has the particular chemical attraction 
known as affinity — oxygen, for example; this combina- 
tion resulting always in the formation of a new com- 
pound which does not have the properties of the ele- 
ments of which it is composed. This union is generally 
accompanied by an evolution of light, and always of 
heat. 

Oxygen is the great supporter of combustion and the 
chemical reactions of atmospheric air are due to the 
presence of this gas in its composition; the nitrogen 
present being inert or passive. 

Chemical Attraction — This force is distinguished from 
other kinds which act within minute distances, by the 
complete change of characters which follows its exer- 
tion, and must, from its very nature, be exerted between 



CHEMICAL ATTRACTION. 99 

dissimilar substances. A good illustration of chemical 
attraction, and one well known to machinists, is that of 
dissolving zinc in muriatic acid to make a soldering 
liquid ; atom by atom it yields to the action of the acid 
until the zinc entirely disappears; as a result there 
remains a liquid having neither the properties of the 
acid nor the zinc— a new compound has been formed. 

A striking illustration of the difference between the 
effects of mechanical intermixture and those of chem- 
ical combination is afforded in the case of ordinary gun 
powder. (17). In the manufacture of this substance, 
the materials of which it is made — viz, charcoal, sul- 
phur and nitre — are separately reduced to a state of 
fine powder ; they are then intimately mixed, moistened 
with water, and thoroughly incorporated by grinding 
for some hours under edge stones ; the resulting mass is 
subjected to intense pressure, and the cakes so obtained, 
after being broken up and reduced to grains, furnish the 
gun powder of commerce. 

In this state it is a simple mixture of nitre, charcoal 
and sulphur. Water will wash out the nitre, bisulphide 
of carbon will take up the, sulphur, and the charcoal 
will be left undissolved. By evaporating the water, the 
nitre is obtained; and on allowing the bisulphide of 
carbon to volatilize, the sulphur remains. If, however, 
we cause the materials to enter into chemical combina- 
tion, all is changed ; a spark fires the powder ; the dor- 
mant chemical attractions are called into operation; a 
large volume of gaseous matter is produced; the char- 



100 COMBUSTION OF COAL. 

coal disappears, and no trace of the original ingredients 
which formed the powder is left. 

The physical and other changes brought about by 
the formation of new compounds — a result of chemical 
attraction — do not destroy the combining elements, but 
simply re-arranges them in another form, and gives to 
the new compound properties not held by any element 
singly. 

It means transformation, not destruction; no matter 
how much the substances may change their form, the 
weight of the new products, if collected and examined, 
will be found to be exactly equal to that of the sub- 
stances before the combination. For example : the com- 
plete combustion of hydrogen and oxygen forms water, 
having properties entirely different from either of the 
two gases. Water may be decomposed, and resolved 
into the two gases of which it was formed. The 
weights, combined or singly, vail in either case be the 
same. 

Whenever substances unite directly with each •other, 
heat is emitted, and varies with the nature of the sub- 
stances between which it is exerted. In general, the 
greater the difference in the properties of the two 
bodies, the more intense is their tendency to mutual 
chemical action ; on the other hand, the chemical attrac- 
tion between bodies having properties closely allied to 
each other is less violent, and graduates so imperceptibly 
into mere mechanical mixture, that it is often impossible 
to mark the limit. 



DEFINITE PROPORTIONS. 



101 



Definite Proportions — The law of definite proportions 
may be stated as follows (17): 

In any chemical compound the nature and the propor- 
tions of its constituent elements are fixed, definite and inva- 
riable. For instance, 100 parts of water by weight con- 
tain 88.9 of oxygen and 11.1 of hydrogen; these gases 
will combine in no other proportions to form water, 
and any excess of either gas will remain unchanged. 

"When two or more compounds are formed of the 
same elements, there is no gradual blending of one into 
the other, as in the case of mixtures, but each 
compound is sharply defined and exhibits properties 
distinct from those of the others, and of the 
elements of which the compounds are composed. 
This is the principle in the law of multiple propor- 
tions. 

There are two compounds of carbon and oxygen 
commonly known as carbonic acid (C0 2 ), and carbonic 
oxide (CO). They may be tabulated, in order to illus- 
trate what has just been said in regard to multiple 
proportions, thus : 



Carbonic oxide. 
Carbonic acid.... 



CO 
C0 2 



CARBON". 
PARTS BY WEIGHT. 



12 
12 



OXYGEN. 
PARTS BY WEIGHT. 



16 
32 



It will be observed that, the quantity of carbon 
remaining the same, the quantity of oxygen must be 
doubled in order to form the other compound, carbonic 



102 



COMBUSTION OF COAL. 



acid. These proportions constitute the only two direct 
inorganic compounds of carbon and oxygen. It is 
usual, in tabulating proportions, to give percentages of 
the composition instead of atomic weights ; transposing 
the above, it would appear thus : 





SYMBOL. 


ATOMIC WEIGHT. 


CARBON. 


OXYGEN. 


Carbonic oxide.... 
Carbonic acid 


CO 

CO, 


2$ 
44 


42.86 
27.27 


57.14 
72.73 



For an extended series illustrating- the law of definite 
proportions of two of the constituents of coal gas, car- 
bon and hydrogen, note the many combining proportions 
in the marsh gas, the olefiantgas, and the benzole series? 
of the products obtained from coal, given on page 95. 

The whole table is one of great interest and value in 
connection with the study of the law of definite or mul- 
tiple proportions, as well as a most valuable contribution 
to the chemistry of coal. 

Law of Equivalents — By this is understood : if a body 
— oxygen, for example — unites with certain other bodies, 
hydrogen, carbon, nitrogen, sulphur, etc., then the quan- 
tities by weight in which the latter substances will com- 
bine with the oxygen, or contain multiples of these 
quantities, they represent in general the proportions in 
which they can unite amongst themselves. 

Hydrogen combines with oxygen in a smaller propor- 
tion than any other known substance, and the numbers 
representing the equivalents of all other bodies may, for 



LAW OF EQUIVALENTS. 



103 



practical purposes, be taken without material error, as 
multiples by whole numbers of the equivalent of hydro- 
gen (17). 

Table XIII. 

Table of Elementary Substances Compiled from the List of " Pro 
ducts Obtained from Coal," together with the Symbol. Spe- 
cific Gravity, Atomic Weight and Equivalent Number of 
Each. 





SYMBOL. 


SPECIFIC 
UKAVITY. 


ATOMIC 
WEIGHT. 


EQUIVALENT NUMBER. 




H~=l 


O=100. 


Bromine 


Br. 
' C 
Cr. 
H 
N 

K 
S 


2.966 

3.52* 

6.000 

.069 

.974 

1.106 

.860 

2.000 


80 

12 

52 

1 

14 
16 
39 
32 


80. 

6. 
26.27 

1. 
14. 

8. 
39. 
16. 


1000. 


Carbon 

Chromium 


75. 

328.38 


Hydrogen 

Nitrogen 


12.5 
175. 


Oxvgen 


100. 


Potassium 


487 5 


Sulphur 


200 







The equivalent number of hydrogen in this table is 
1, and as one part of hydrogen is united in water with 
exactly eight parts of oxygen, the equivalent number of 
oxygen is 8. The supposed value of a table like this 
is, that it serves to show the quantities of other elements 
which unite with eight parts of oxygen, and it also 
indicates the simplest proportions in which they can 
unite with each other. 

The equivalent numbers, as given in this table, are 
seldom used, and the reason why their discontinuance 

'•'Specific gravity of a pure diamond. 



104 COMBUSTION OF COAL. 

was brought about was explained in the section on 
atomic and molecular weights, page 8. 

Energy of Chemical Separation — A combustible body 
like coal may be taken as a fair representative of poten- 
tial energy, because it occupies a position of advantage 
over a non-combustible body in this, that it will unite 
with another body for which it has chemical affinity 
like oxygen, and this energy of position leading as it 
can in this case, to a process of chemical separation 
during the act of burning, in which we have potential 
energy or the energy possessed by the coal before igni- 
tion, and, the energy due to molecular activity by reason 
of the act of combustion, or the energ} T of motion 
changed or transmuted into another form of energy 
represented by heat ; which, if we choose, may then be 
again transformed into almost every other form of 
energy, by suitable trains of mechanism, or other meth- 
ods; remembering, however, that every time a transfor- 
mation takes place there is always a tendency to pass, 
at least in part, from a higher or more easily transform- 
able to a lower form. 

The energy of chemical separation, when produced 
by the combustion of coal, is always intense, and as the 
observed effects are so much below the theoretical value 
ascribed to the fuel, it would seem as if for once the 
law — if there is one — of conservation of energy was at 
fault. But this is not the case. Our methods of manip- 
ulation are so wasteful, and the ordinary construction 
of furnaces so much at variance with the ideal furnace 



NATURE OF COMBUSTION. 105 

— whatever that may be — that a large percentage of 
waste can be directly accounted for. 

One thing with reference to the energy of chemical 
separation is certain, and that is, that any given quan- 
tity of carbon or other combustible, under given condi- 
tions, will always produce the same quantity of heat. 

The Nature of Combustion — When a piece of rich 
bituminous coal is thrown upon a brisk open fire, a par- 
lor grate for example, it will be observed that physical 
changes in this piece of coal rapidly occur. First, a 
disengaging of small particles of coal, which are often 
projected from the larger piece with some violence; 
then a swelling or puffing out of the exterior surfaces of 
the coal; jets of smoke issuing here and there, proving 
themselves to be rich in inflammable gases, for soon 
they burst into a flame, often white and intensely bril- 
liant near the coal, fading into a brownish yellow flame, 
terminating in smoke. Presently the piece of coal will 
show indications of cleavage and may split itself into 
two or more parts. Sometimes this will go on until the 
whole lump disintegrates, or goes to pieces; at other 
times, it will continue to swell, expanding to much 
more than its original volume, giving off its gases, and 
a caking process is undergone until the whole mass is 
apparently fused together, after which, the volatile por- 
tions of the coal having been expelled and burned, the 
remaining portion assumes the general incandescent 
state of the body of the fuel in the grate, disappear- 
ing little by little through the action of some unseen 



106 COMBUSTION OF COAL. 

agency, until it yields up all its combustible substance, 
and aslies alone remain, to mark the completeness of the 
change. 

It would be interesting to know what became of 
this piece of coal. If, instead of throwing the whole 
piece in the fire a portion had been retained, it would 
probably have yielded by proximate analysis, 

PER CENT. 

Fixed carbon 60 

Volatile combustible matter 32 

Water 3 

Ash 5 

100 

The thirty-two per cent, of volatile matter would, 
upon farther analysis, be found to consist of 

Carbon ; Nitrogen ; 

Hydrogen ; Sulphur. 

Oxygen; 

The particular forms in which these elements are 
usually found to be grouped, are, 

Marsh gas CHi 

Olefiant gas C 2 H 4 

Hydrogen H 

Carbonic oxide CO 

Carbonic acid C0 2 

Nitrogen N 

Ammonia NH ;i 

Sulphurous oxide S0 2 

Bisulphide of carbon CS 2 

Water H 2 



NATURE OF COMBUSTION. 107 

and many hydrocarbons not given, the combinations 
of these two elements being exceedingly numerous; of 
the above, nitrogen, carbonic acid, ammonia and water, 
are not supporters of combustion. 

In general, carbon and hydrogen are the elements 
meant when the ordinary term fuel is used, and oxygen 
is the agent by which they are made to yield up their 
heat. It is the chemical union of these elementary sub- 
stances which we shall designate as the particular form 
of combustion meant wherever the word occurs in this 
work. 

The exact nature of combustion is not easily stated. 
It has been shown elsewhere that coal is composed of 
ultimate particles called atoms, also that atoms of differ- 
ent substances are attracted toward each other. Both 
the carbon and hydrogen in coal have an affinity for 
oxygen ; before they unite it is necessary that certain con- 
ditions be fulfilled. In the case of coal the oxygen has 
no apparent effect on it at ordinary temperatures, but 
once the coal is heated to the point of ignition the oxy- 
gen will unite with it, and Prof. Tyndall's theory is: 
" Oxygen having a choice of. two partners, closes with 
that for whieh it has the strongest attraction. It first 
unites with the hydrogen and sets the carbon free. 
Innumerable solid particles of carbon thus scattered in 
the midst of burning hydrogen are raised to a state of 
incandescense. The carbon, however, in due time, closes 
with the oxygen, and becomes, or ought to become, car- 
bonic acid." The heat and light produced by the burn- 
ing of coal are due, according to his theory, to the 



108 COMBUSTION OF COAL. 

collision of atoms which have been urged together by 
their mutual attractions. 

A necessary condition to the burning of coal is, that 
there be a considerable mass of it ignited or burning in 
order to prevent too rapid cooling ; an isolated piece of 
coal will not burn in the open air, because the tempera- 
ture will soon fall below the point of ignition, and, as a 
consequence, chemical action will cease ; but an ignited 
mass of coal under certain conditions — the combustion 
chamber of a stove, or the grate surface of a furnace, 
for example — will give off great heat, the intensity of 
which will depend upon the quality and amount of coal 
burned, but once the hydrogen and carbon having united 
with oxygen, and formed by their union, water and 
carbonic acid, respectively, their mutual attractions are 
satisfied, and all the heat has been given off that is pos- 
sible under any conditions. 

"Whatever may be the real nature of that property 
of matter called chemical affinity (34), it seems to be a 
general law that bodies most opposed to each other in 
chemical properties evince the greatest tendency to 
enter into combination, and when these chemically dis- 
similar bodies are brought together under favorable con- 
ditions, one very important fact is clearly established 
with regard to it, and that is, that this chemical union is 
always accompanied by the production or the annihila- 
tion of heat. The measurement of the quantity of heat 
produced by a given amount of chemical action is a 
problem not easily solved, but it may be expected that. 
if a definite quantity of carbon be burned under given 



NATURE OF COMBUSTION. 109 

circumstances, there will be a definite production of heat 
(26), that is to say, a ton of coals or of coke, when 
burned, will give us a certain number of heat units, and 
neither more or less. 

CONDITIONS NECESSARY TO COMBUSTION. 

Carbon, hydrogen, etc., will combine with oxygen in 
certain definite proportions only. The combining ele- 
ments must be in immediate contact, not the contact 
which we usually mean when powdered or liquid sub- 
stances are mixed together, but the contact which chem- 
ical affinity denotes, and this contact must be at a 
certain temperature in order to produce combustion. 
Carbon and oxygen will remain in mere physical con- 
tact any length of time, but suppose a single atom of 
carbon be heated red-hot, combustion will begin at once 
and continue until the supply of either one of the ele- 
ments is consumed by the other. There is no element 
in nature which has not an affinity for some other 
element, but it does not follow that the affinity 
existing between such bodies shall be accompanied 
by the evolution of light and heat which are so prom- 
inent in the combustion of coal. The oxidation or 
corrosion of iron, for example, in which a body of iron 
in a moist atmosphere combines with oxygen and hydro- 
gen, resulting in the formation of a new compound, 
does so with a slight evolution of heat, but none at all 
of light. 

All solid substances, when heated sufficiently high, 
emit light. This light may be more or less intense, 



110 COMBUSTION OF COAL. 

according to the temperature of the heated solid. The 
temperature at which bodies begin to emit red, or the • 
feeblest light in the dark, is about 700° Fahr., and 
increases in intensity and brilliancy with the higher - 
degree of heat, until it passes successively through the 
gradations, red, orange, yellow and white heat, which is 
the highest that can be attained in the furnace ; bodies 
in these states are said to be incandescent or ignited. 

Combustion and ignition are not the same thing. 
The ignition of solids is a source of light: the combus- 
tion of solids is a source of heat. Light and heat, 
though apparently governed by the same laws, are not 
identical. The combustion of hydrogen with oxygen 
produces a most intense heat, yet the light emitted is so 
feeble as to be scarcely visible in daylight; if, however, 
a piece of lime be introduced into the flame it becomes 
so intensely brilliant that the eye can not bear it. This 
piece of lime can not have a higher, nor indeed so high 
a temperature as the flame itself. The particles of lime 
in this high temperature become incandescent or ignited, 
and are the source of the light — if the lime be removed, 
the intensity of the light is gone, but the heat remains 
the same ; so it would appear that ignition is the glow- 
ing whiteness of a body caused by intense heat, or, it is 
a consequence of combustion instead of a factor in it, 
the particles which give off the light passing away 
mechanically, without change of chemical constitution ; 
on the other hand, it is the chemical change in the 
bodies themselves, and the formation of new com- 



FLAME. Ill 



pounds, which characterizes combustion, in whatever 
form it may appear. 

That the presence of two bodies is necessary to com- 
bustion, is very neatly illustrated in the case of a glass 
tube containing a gas, through which an electric spark 
is to pass in order to determine its spectrum. If a single 
gas would burn in a hermetically-sealed tube upon the 
application of a spark, these tubes would, after the first 
experiment, be unfit for the purpose designed; yet the 
spark may be passed through, the spectrum determined, 
but the gas remains unchanged. 

We have already seen, in the first part of this chapter, 
that if combustible substances, such as charcoal, sulphur 
and saltpetre, be intimately mixed together, and the 
temperature of a portion of the mass be raised to the 
point of ignition, the combustion is so rapid and violent 
that it is called an explosion. The combustion in this 
case is carried on independently of the oxygen of the 
atmosphere. 

Flame — In the burning of wood and bituminous 
coal, flame is a marked characteristic, less so in semi- 
bituminous, and almost entirely wanting in the burning 
of anthracite and charcoal. Ordinary flame is gas or 
vapor, of which the surface, in contact with the atmos- 
pheric air, is burning with the emission of light. The 
structure of flame, in general, may be understood by a 
careful study of that produced by an ordinary lighted 
candle, an illustration of which is given in figure 1. It 



112 



COMBUSTION OF COAL. 



A 



C 



\ 



\ \ 



'B\\ 






— 



Figure 1. 



consists of three separate portions: the 
inner portion, A, nearest to and surround- 
ing the wick, is a vapor of the material of 
which the candle is composed; the second 
portion, B, is a luminous cone which envel- 
opes A, and is that portion of the flame 
in which chemical action is begun, but 
which does not seem to be completed until 
the third portion of the flame, marked C, 
is reached. It will be understood, of course, 
that flame does not consist of cones, or 
envelopes in such contrast as the engraving 
would seem to indicate; this is for the 
purpose of illustration only. The explanation of the 
structure of this flame carries us back, to first of all, the 
application of heat to melt and vaporize the combustible 
material in the wick, and then ignite it. The consti- 
tuents of the candle being carbon and hydrogen, the 
latter being more easily disengaged and set free than 
the former, and having a greater attraction for oxygen 
than carbon, unites with it first, and forms a hydro- 
carbon flame in which the hydrogen is burning, whilst 
the particles of solid carbon in the flame are heated to 
a point of incandescence, and produce the light-giving 
quality of the flame. It is quite probable that the com- 
bustion of the carbon is completed, if at all, in the 
outer envelope C, in contact with the atmospheric air 
from whence the supply of oxygen is had. It is not- 
known how far the oxygen penetrates the flame, but- 
judging from its great height, as compared with its 



FLAME. 113 



diameter, it is quite probable that it is largely, if not 
entirely, confined to the surface of the cone B ; this is- 
inferred from the soot deposited, and lower heat 
observed, when a piece of card-board is passed through 
the flame just above the wick, indicating an incomplete' 
combustion, which is not observed when the card-board 
is held in the apex of the outer cone. 

The structure and appearance of flame are modified- 
somewhat by the density of the gaseous matter burning, 
and by the pressure of the air in contact furnishing the 
oxygen. This is quite noticeable in the case of steam 
boiler furnaces operated with, and then without, a* 
forced draft. Firemen, as a rule, judge of the complete- 
ness of combustion by the appearance of the surface or 
flaming portion of the fire. This is a guide which often 
serves a good purpose, yet it does not reveal the whole 
secret. It is possible to tell how nearly the prevention 
of smoke is accomplished, but carbonic oxide, that 
arch-enemy of economy in furnace combustion, may 
still be there. The admission of air in the furnace 
above the grates and near the fuel, serves a useful pur- 
pose in igniting the carbonic oxide as it rises from the 
mass of burning coal ; this flame, as exhibited in the 
burning of anthracite coal or coke, has a bluish tinge, 
which may easily be distinguished from the brownish- 
yellow flame produced by the burning of coal rich in 
hydro-carbons. However, too much dependence must 
not be placed on the mere appearance of flame, either in 
its length or color. 
(9) 



114 COMBUSTION OF COAL. 

Pure hydrogen gas, which yields a most intense heat, 
burns almost without visible flame; it is so faintly blue 
as to be scarcely luminous in full daylight. Perhaps the 
best illustration of colorless name is shown in the ope- 
ration of the well known Bunsen gas-burner as fitted 
for laboratory uses ; here, the glowing solid particles of 
carbon, which give character to hydrocarbon flames, are 
almost entirely wanting, having been destroyed by 
intense heat and quick combustion. 

It would be impossible to give a description of flame 
which would be of the slightest service in determining 
what is going on in the furnace. There are few other 
than experienced persons who can tell the color of flame 
in a mass of incandescent fuel ; but, allowing this much, 
to it must be added a knowledge of color and form of 
flame characteristic of known combustibles when per- 
fectly or imperfectly burne ; this only leads into a 
labyrinth of difliculty and uncertainty which we may 
well keep out of, and endeavor by other means, much 
more certain and reliable, to arrive at the facts sought 
after. This, of course, does not apply to the observa- 
tion of the oxidizing of foreign substances, so beauti- 
fully illustrated in the Bessemer process, where the 
flame emitted is constantly changing until the impuni- 
ties are gone, and the brilliant and characteristic light 
of iron alone remains. 

RECENT STUDIES OF LUMINOUS FLAMES (24). 

"For a long time Sir Humphrey Davy's explanation 
of the luminosity of flames — that it was due to the 



FLAME. 115 



presence of highly-heated solid particles — sufficed for 
all observed phenomena. A serious blow to its suffi- 
ciency was given, however, when Frankland discovered 
that certain flames were luminous under conditions 
which left no reason for supposing that solid matter 
could be present. For instance, hydrogen and carbon 
monoxide, burned in oxygen under a pressure of ten to 
twenty atmospheres, yield a luminous flame giving a 
continuous spectrum. So likewise the non-luminous 
flame of alcohol becomes bright when the pressure is 
increased to eighteen or twenty atmospheres. Frank- 
land inferred from experiments like these that the 
luminosity of flames was due rather to the presence of 
the vapors of heavy hydrocarbons, which radiate white 
light, than to incandescent solid matter. 

" Still further doubt of the prevalent theory was 
raised by the experiments of Knapp, which proved that 
the diminished luminosity of a flame on the admission 
of air could not be due, as had been supposed, to an 
oxidation of the carbon suspended in the luminous gas, 
since the same effect was produced when nitrogen or 
carbon-dioxide, or other indifferent gas, was used as a 
diluent. 

" Stein and Blochmann attributed this effect to the 
direct influence of the diluting gases in separating the 
particles of carbon, so that the oxygen of the air might 
unite with them more quickly than under the ordinary 
circumstances of combustion. Wibel held, on the con- 
trary, that the diminished luminosity was due entirely 
to the absorption of heat by the diluting gas, and sup- 



116 COMBUSTION OF COAL. 

ported his view by some very ingenious experiments. 
The correctness of this conclusion has been, in turn, 
controverted by the later experiments of Stein and 
Heumann, particularly the latter, which seem to show 
that the diminished luminosity consequent upon dilution 
is due not solely to dilution nor wholly to the cooling 
action of the added gases, but to both these causes acting 
together and frequently supplemented by a third cause — 
namely, the energetic destruction of the luminous 
material by oxidation. Heumann's experiments, which 
have been particularly ingenious and careful, lead to the 
following results: That hydrocarbon flames, which 
have lost their luminosity by the withdrawal of heat, 
become luminous again by the addition of heat; that 
flames rendered non-luminous, by dilution with air or 
indifferent gases, become luminous again on raising 
their temperature; that flames rendered non-luminous 
by excess of oxygen, which brings about energetic 
oxidation of the carbon, are rendered luminous again 
by diluting., the oxygen in different cases. In most 
cases of diminished luminosity two or all of these causes 
are at work. 

"Another unsettled question with regard to flames 
has been the cause of the non-luminous space between 
the opening of a gas burner and the flame, or between 
the wick of a candle and the luminous envelope. Bloch- 
mann attributed it to the inability of the surrounding 
air to mix at once with the stream of gas so as to make 
it combustible. Benevines, on the other hand, thought 
the dark space due to* the mechanical action of the 



RATE OF COMBUSTION. 117 

issuing gas, whereby the air is driven to a distance from 
the orifice of the burner — greater or less, according to 
the pressure on the gas, leaving a space wherein the gas 
is deprived of the requisite amount of oxygen, and 
consequently remains unburned. Both these explana- 
tions are shown to be insufficient by the single circum- 
stance that a flame never directly touches any cold body 
held within it. In all such cases Heumann finds an 
explanation of observed conditions in the cooling effect 
of its surroundings — burner, wick, cold iron, or what 
not — upon the gas. For a certain space around the 
cooling body the gas remains at a temperature too low 
for ignition. 

"Where the gas issues under high pressure, or is 
greatly diluted, the distance of the flame is attributed 
partly to this same cooling action of its surroundings, 
but more especially to the fact that the velocity of the 
stream of gas in the neighborhood of the burner is 
greater than the velocity of the propagation of ignition 
within the gas." 

Rate op Combustion — By this is understood the 
weight of fuel that can be burned in a given furnace in 
a given time, but, as applied to steam boilers, it means 
the number of pounds of coal or coke which can be 
burned per square foot of grate surface per hour. 
Sometimes the rate of combustion is expressed as 
pounds of net combustible; by this is meant the pounds 
of fuel burned, deducting the ashes and other incom- 
bustible matter. 



118 COMBUSTION OF COAL. 

The following table is from Professor Rankine's 
"Steam Engine," showing the rate of combustion of 
English coals, with a chimney draft ; expressed in 
pounds burned per hour, per square foot of grate sur- 
face : 

POUNDS. 

1. Slowest rate of combustion in Cornish boilers 4 

2. Ordinary rate 10 

3. Ordinary rates in factory boilers 12 to 16 

4. Ordinary rates in marine boilers 16 to 24 

5. Quickest rates of complete combustion of dry coal, 

the supply of air coming through the grate only.. 20 to 23 

6. Quickest rates of complete combustion of caking 

coal, with air-holes above the fuel to the extent 

of 1-36 of the area of the grate 24 to 27 

7. Locomotives 40 to 120 

Iii the experiments carried out by The Societe Alsa- 
ciennes de Constructions Mecaniques, Mulhouse, the quan- 
tity of Ronchamp coal burned per square foot of grate 
surface in a Lancashire boiler was, 

For ordinary tiring 18.5 pounds. 

For slow firing 10.15 pounds. 

For heavy firing 19.01 pounds. 

the rate of combustion between slow and heavy firing 
being almost 2 to 1; in regard to results: the quantity 
of water evaporated being expressed in equivalent 
evaporation at atmospheric pressure, and from a tem- 
perature of 212° Fahr., was, 

For ordinary firing 8.94 pounds of water. 

For slow firing 9.29 pounds of water. 

For heavy firing 9.06 pounds of water. 



RATE OF COMBUSTION. 



119 



During the Centennial Exhibition at Philadelphia, 
1876, eight sectional boilers were tested : 

1. To ascertain the capacity; 

2. To ascertain the economy, of each. 

The following table is collated from the published 
reports of the trials : 

Table XIV. 

Showing the Number of Pounds of Net Combustible (Lehigh Coal) 
Burned per Square Foot of Grate Surface per Hour, with 
Natural Draught. 





GRATE 
AREA 
IN- 
SQUARE 
FEET. 


FOR CAPACITY. 


FOR ECONOMY. 


REFERENCE 

LETTER 

DESIGNATING 

BOILER. 


POUNDS 

OF 
COMBUS- 
TIBLE 

PER 
HOUR. 


RATE OF 

COMBUS- 
TION IN 
POUNDS 
PER 
HOUR. 


POUNDS 

OF 
WATER 
EVAPOR- 
ATED PER 
HOUR, 
FROM 
AND AT 
212°. 


POUNDS 

OF 
COMBUS- 
TIBLE 

PER 
HOUR. 


RATE OF 
COMBUS- 
TION IN 
POUNDS 
PER 
HOUR. 


POUNDS 

OF 
WATER 
EVAPOR- 
ATED PER 
HOUR, 
FROM 
AND AT 

212°. 


A 
B 

C 

D 
E 
F 
G 
H 


42. 

23. 

15.41 

42. 

27.5 

30. 

44.5 

36. 


613.91 
378.07 
213.08 
490.77 
410.52 
373.25 
622.87 
478.40 


14.62 
16.44 
13.83 
11.69 
14.93 
12.44 
14.00 
13.29 


9.15 

9.89 

11.06 

10.44 

8.40 

9.97 

10.33 

9.57 


469.57 
260.16 
166.13 
341.71 
270.81 
248*59 
3 5.57 
318.41 


11.18 

11.31 

10.78 

8.14 

9.85 
8.29 
8.89 
8.84 


10.83 
10.93 
11.99 
12.09 
10.31 
10.04 
11.82 
10.62 



For anthracite coal, the ordinary rate of combustion 
under stationary boilers may be taken at from eight to 
sixteen pounds per square foot of grate per hour. 

For bituminous coal, from ten to twenty pounds. 



120 COMBUSTION OF COAL. 

In locomotives, Mr. Forney (11) gives the maximum 
rate of combustion at about one hundred and twenty- 
five pounds of coal on each square foot of grate surface 
per hour. 

Temperature of Fire — The temperature of combus- 
tion is conditioned upon 

The nature of fuel burned. 

The nature of the products of combustion. 

The quantity of the products of combustion. 

The specific heat of the gases present in the furnace resulting 
from combustion; this includes the quantity of air present at the 
moment of combustion in order to render it complete. 

The principal products in the furnace after the com- 
bustion of coal are, 

Carbonic acid. ] 

Carbonic oxide. 

Nitrogen. 

Air furnished in excess, and unconsumed. 

Gaseous steam. 

In the complete combustion of one pound of carbon 
we have 

Carbon 1 

Oxygen 2.67 

Total 3.G7 pounds of carbonic acid. 

And in addition to this there would be present in the 
furnace 8.94 pounds of nitrogen left after the separation 
of the oxygen from the atmospheric air. We have 
then, 



TEMPERATURE OF FIRE. 121 



PRODUCTS. 

Carbonic acid 

Nitrogen , 


POUNDS. 

3.67 X 

8.94 X 


SPECIFIC 
HEAT. 

.2104 = 
.244 = 

Total, 


HEAT 
UNITS. 

.794 
2.181 




.4/ 


2.975 



heat units absorbed in raising the temperature of the 
products of combustion one pound of carbon 1° Fahr. 
The combined weight of the two products are 
12.61 pounds. 



Then, 



Heat units 2.975 

= .236 

Pounds 12.61 



their mean specific heat. 

The total heat of the combustion of carbon is 
14,544 heat units; divide this by the 2.975 heat units 
absorbed, we have, 



4544 4889° Fahr. 



2.970 



as the highest theoretical temperature attainable by 
the complete combustion of one pound of carbon. 

This is allowing 11.61 pounds of air per pound of 
carbon, the minimum theoretical limit. 

Suppose that eighteen pounds of air are admitted 
to the furnace, instead of twelve pounds (11.61), and 
that the combustion is complete, the temperature and 
products will then be, 

Carbon 1 

Oxygen 2.67 



122 COMBUSTION OF COAL. 

Nitrogen 8.94 

Air 6.39 

19.00 
We then have, 

SPECIFIC HEAT 

PRODUCTS. POUNDS. HEAT. UNITS. 

Carbonic Acid 3.67 X .2164= .794 

Nitrogen 8.94 X .244 = 2.181 

Air, uncombined 6.39 X .2377= 1.519 

Totals 19.00 4.494 



Then, 

4.494 
19. " 

14.544 



.237 mean specific heat. 



— 3236° Fahr. 
4.494 

the temperature of the fire being 1653° less than the first 
example, showing a loss of 33.81 per cent. 

If double the qauntity of air (twenty-four pounds) 
had been present in the furnace over that needed for 
combustion the temperature would have been about 
2450° Fahr. These examples suffice to show the loss 
sustained by the admission of too much air in the 
furnace. 

It is scarcely necessary to remind the reader that the 
combustion of carbon is here intended, and not that of 
coal; this is mentioned, merely, to explain an apparent 
discrepancy in the next table. 



AVAILABLE HEAT OF COMBUSTION. 



123 



Table XV. 

Showing the Weight and Specific Heat of the Products of Com- 
bustion, and the Temperature of Combustion (2). 



ONE POUND OF COMBUSTIBLE. 



Hydrogen 

Olefiant Gas 

Coal (average) 

Carbon, or Pure Coke. 

Alcohol 

Light Carbureted Hydrogen 

Sulphur 

Coal, with Double Supply of Air.. 



GASEOUS 


PRODUCTS FOR 1 LI 






HEAT TO 






RAISE 




MEAN 


TEMPER- 


WEIGHT. 


SPECIFIC 


ATURE 




HEAT. 


ONE 

DEGREE 

FAHR. 


POUNDS. 


WATBE=1. 


UNITS. 


35.8 


.302 


10.814 


15.9 


.257 


4.089 


11.94 


.246 


2.935 


12.6 


.236 


2.973 


10.09 


.270 


2.680 


18.4 


.268 


4.933 


5.35 


.211 


1.128 


22.64 


.242 


5.478 



TEMPERATURE 

OF 

COMBUSTION. 



FAHR. 
5744° 

5219 

4879 
4877 
4825 
4760 
3575 
2614 



RATIO. 

100 
91 
85 
85 
84 
83 
62 
45 



Available Heat of Combustion — The available heat 
of combustion of one pound of a given sort of fuel, is 
that part of the total heat of combustion which is com- 
municated to the body to heat which the fuel is burned ; 
for example, to the water in a steam boiler. 

The efficiency of a furnace, for a given sort of fuel, is 
the proportion which the available heat bears to the 
total heat, when the given sort of fuel is burned in the 
given furnace. 

The word "furnace" is here to be understood to 
comprehend, not merely the chamber in which the 
combustion takes place, but the whole apparatus for 
burning the fuel and transferring heat to the body to be 



124 COMBUSTION OF COAL. 

heated, including ash-pit, air-holes, flame-chamber, flues, 
tubes, and heating surface of any kind, and chimney. 

The theoretical heat of any given fuel is easily 
determined, its proximate or elementary analysis being 
known; but the actual available heat is not so easily 
arrived at, and can only be determined by a series of 
more or less elaborate experiments or trials in actual 
use. In steam boilers the efficiency of the furnace is 
measured by the pounds of water evaporated per pound 
of coal burned on the grate, under known conditions. 
This will always be found to be below the theoretical 
quantity, and may be accounted for in many ways. 

Heat, like water, or steam, must flow from a higher 
to a lower level in order to become available, and in 
this flow or transfer there is a loss, which is explained 
in the article on the dissipation of energy. 

There is a loss due to the radiation of heat from the 
sides of the furnace; this may be prevented in part by 
building hollow walls around the furnace. 

There is a loss in the use of cold instead of heated 
air for supplying the oxygen to the burning fuel. This 
may be remedied in part by forcing the air through the 
hollow space left between the two walls, as suggested in 
the preceding paragraph. 

There is a loss occasioned by the difference of tem- 
perature between the escaping gases and that of the 
atmosphere necessary to produce natural draft. This 
may be largely overcome by using a forced draft, and 
dispensing with a chimney altogether, except one suffi- 
cient to get rid of the noxious gases ; in which case it 



AVAILABLE HEAT OF COMBUSTION. 125 

will act as an outlet only, the gases being forced into the 
open air by a pressure behind them, and thus more heat 
may be abstracted from them than if the temperature 
were used for assisting the draft. 

There is a loss by the waste of unburned fuel pass- 
ing off as smoke, and that falling through the grates 
into the ash-pit unconsumed. 

There is loss by imperfect combustion, that is, loss 
by the formation of carbonic oxide instead of carbonic 
acid. 

The consideration of each of these forms of loss has 
been undertaken elsewhere in this volume, and need not 
be repeated here. There is no method by which the 
efficiency of a furnace can be exactly determined, 
except by an experimental test in actual service. 

The quantity of water evaporated from and at 212° 
per pound of coal, varies in ordinary practice from six 
to ten pounds ; ten pounds is considered a very fair 
evaporation, and is probably much above the average ; 
this is about seventy-one per cent, of the theoretical, if 
we assume fourteen pounds, as the average theoretical 
evaporation power of good coal and coke. 

With inferior coal the results would be far below 
this; the quality of the coal or coke used must be taken 
into account, as well as the construction of the furnace, 
and to obtain the highest results, the furnace should 
have its details arranged with special reference to the 
burning of a particular fuel, as may be found after a 
trial, the best and most economical arrangement for 
that fuel. 



CHAPTER VI. 



AIR REQUIRED FOR FURNACE COMBUSTION. 

Proportions in which Oxygen unites with Carbon and Ffydrogen — 
Air required for different Fuels — Heated Air for Combustion — 
Temperature of Air supplied to Blast Furnaces — The Hoffman 
Kiln — Berthier's Theory in regard to Heated Air — Peclet's 
Observations — Prideaux' Estimation of the Value of Heated 
Air — Difficulties in Heating or Cooling Air — Proportions of Fire- 
Brick to Fuel burned in the Siemens Regenerative Furnace — 
Ponsard Furnace. 

The conditions under which coals are burned are so 
various that no exact quantity of air can be specified 
which will supply oxygen enough for complete combus- 
tion, and still preserve the minimum dilution of gases 
passing from the furnace into the chimney. The quan- 
tity of oxygen required for the complete combustion 
of any given quantity of carbon or hydrogen has been 
experimentally determined, and is well known : the 
quantity of oxygen present in atmospheric air being 
constant, the process of determining the amount of air 
required for the complete combustion of either of these 
two substances is quite simple. 

One pound of hydrogen gas requires eight pounds of 
oxygen for its complete combustion ; this requires about 
thirty-six pounds of air to furnish it; the product of 
this combustion being water H, 0. 

One pound of pure carbon (not coal) requires two 
and two-thirds pounds of oxygen for its complete com- 



AIR REQUIRED FOR FURNACE COMBUSTION. 



127 



bustion, requiring about twelve pounds of air, the pro- 
duct of combustion being carbonic acid, C0 2 . 

One pound of pure carbon (not coal) when only par- 
tially or rather imperfectly burned, so as to yield as a 
product carbonic oxide, CO, instead of carbonic acid, C0 2 , 
requires one and one-third pound of oxygen, furnished 
by about six pounds of air. 

The following table, by Prof. Rankine (22), shows 
the theoretical quantity of air required for the different 
fuels of which the analyses are furnished : 



Table XVI. 



FUEL. 


CARBON. 


HYDROGEN 


OXYGEN. 


AIR 
REQUIRED. 


I. Charcoal — from wood... 


0.93 

80 

0.94 

0.915 

0.87 

0.85 

0.75 

0.84 

0.77 

0.70 

0.58 

0.50 

0.85 






11.16 


Charcoal — from peat.... 
II. Coke — good 






9.6 






11.28 


III. Coal — anthracite 

Coal — dry bituminous... 
Coal — caking 


0.035 

0.05 

0.05 

0.05 

O.0G 

0.05 

0.05 

0.06 


0.026 

0.04 

0.06 

0.05 

0.08 

0.15 

0.20 

0.31 


12.13 
12.06 
11.73 


Coal — caking 


10.58 


Coal — cannel 


11.88 


Coal — dry, long flaming 
Coal — lignite 


10.32 
9.30 


IV. Peat — dry 


7.68 


V. Wood — dry 


6.00 


VI. Mineral Oil 






15.65 











The quantity of air, as shown in the above table, 
represents the number of pounds required for the com- 



128 COMBUSTION OF COAL. 

plete combustion of one pound of the fuel named. The 
intermediate columns show the proximate constituents 
of the fuel. 

The average number of pounds of air required per 
pound of coke and coal, appears, from the above table, 
to be a little less than 11.5 lbs. It is unnecessary for 
practical purposes to compute the air required for the 
combustion of fuel to a great degree of exactness; and 
no material error is produced if the air required for the 
combustion of any kind of coal and coke used for fur- 
naces is estimated at twelve pounds per pound of fuel. 
This is to be understood as the theoretical quantity : 
practically, about twice this amount is supplied ; it may 
be approximately stated that, three hundred cubic feet, 
or twenty-four pounds of air, are supplied to burn one 
pound of coal, in boiler and heating furnaces as ordi- 
narily constructed. 

HEATED AIR FOR COMBUSTION (8). 

" Nearly all the processes in actual use for economiz- 
ing fuel have for their leading principle that of pre- 
heating the air for combustion. This is a pregnant fact, 
of which many instances can be found. When Neilson 
made his invention, or rather discovery, in 1829, he began 
with a temperature in the blast furnace of 50° Fahr., and 
gradually, in succeeding years, raised it to 600° Fahr. 
By 1860 this was further increased to 750° and 800°, and 
from 1854 to the present time it has progressed up to 
1,100°, 1,400°, and more. To heat the great volume of 
air for a large blast furnace some twenty thousand square 



HEATED AIR FOR COMBUSTION. 129 



feet of fire-brick have to be actively employed. A gas 
furnace is simply a physical impossibility without using 
air raised very considerably in temperature above that 
of the atmosphere ; and this was very soon found out by 
the first experimenters. The Hoffman kiln, which has 
revolutionized the brick trade, is highly economical in 
fuel, mainly because the air for combustion is intensely 
heated by first passing through the already burnt, incan- 
descent bricks. In Siemens' regenerative furnaces, and 
in the furnaces with direct-acting regenerators of the 
French engineer, Ponsard, the air and gases for combus- 
tion are brought to high temperatures by being conveyed 
past considerable surfaces of brick, heated by the escap- 
ing fire-gases. In Boetius ? direct-acting gas furnaces 
the air is heated by being passed through passages in 
the brick wall of the producer and other portions of 
the furnace. In Ireland's and in Ivrigar and Grothe's 
cupolas the blast is heated before being allowed to mingle 
with the products of combustion. It is only by the 
application of Dr. Geisenheimer's plan of using very hot 
blast that it is possible to burn American anthracite in 
the blast furnace. The functions of the deflector and 
the fire-brick arch now used in locomotive engines for 
burning coal, mainly consist in heating the atmospheric 
air and gases for combustion. On the London, Brighton 
and South Coast Railway this action is intensified by 
working with the ash-pan almost entirely closed up. A 
leading feature in Mr. T. Symes Prideaux's contrivances 
for economizing fuel consisted in pre-heating the air. 

Several contrivances of smaller fame could be cited as 
(10) 



130 COMBUSTION OF COAL. 

depending for their success on the use of more or less 
heated air, such as oue or two forms of puddling fur- 
naces and furnace doors. The leading feature of Mr. 
"W. Gorman's gas-furnace is that of heating the air for 
'combustion by means of the escaping fire-gases. How- 
atson's puddling and heating furnaces, of which a great 
number were said to have been set up a few years ago, 
is another instance of the application of heated air, as is 
also in great measure that of Mr. Price. A furnace 
which has been described as the Newport puddling fur- 
nace may be said to be on a partially regenerative 
system. 

" One obvious reason to account for the effect of the 
heated air in raising the intensity of combustion, is the 
mere fact of the attendant elevation of temperature. A 
current of air sufficiently hot can set wood or coal on 
fire. But there are several more recondite reasons than 
this. In the first place, a very high temperature of the 
air for combustion acts as a corrective whenever too 
little or too much air is introduced. The French savant, 
Berthier, gave another reason, which would partly 
account for several points noticable in the practical 
working of furnaces. It is based on the very probable 
hypothesis that the chemical affinity of heated air 
for carbon is much greater than that of cold air. As 
observed by Peclet, one consequence is, that when heated 
air is employed, it is deprived of oxygen within a very 
short travel. The combustion is thereby more concen- 
trated and localized at the focus where the heat has to 
be applied and to do its work. At the spot required 



HEATED AIR AND CHEMICAL ACTION. 131 

the heat is higher, and at the same time beyond it lower. 
These two circumstances are favorable to the economy 
of fuel, for combustion and high temperature beyond 
the point where heat has to be applied are useless. It 
has thus been found in practice that the greater the 
affinity of any fuel for oxygen, the lower need be 
the temperature of the air. It is hence used at a 
lower heat in charcoal furnaces than in coke blast 
furnaces, and less in the latter than in furnaces fed 
with anthracite. This explains the fact, which has been 
found on trial, that a reverberatory furnace, supplied 
with hot air at the grate only, has actually been 
found to have its efficiency diminished, and not 
increased. The gaseous combination or chemical union 
being thereby accelerated, the combustion takes place 
more on the grate and less in the body of the furnace, 
where the actual work has to be done. 

HEATED AIR AND CHEMICAL ACTION. 

"While heating the air for combustion intensifies the 
chemical affinities between the air and the fuel, the pro- 
cess offers another most effective means of diminishing 
the consumption of fuel, and of almost indefinitely 
increasing the intensity of the fire. By applying the 
fire-gases — which are useless where they are only equal 
in temperature to the goods to be heated — to pre-heat- 
ing the air for combustion, an actual recuperation, 
returning, or carrying back, of the heat is caused. 
This amount saved can be exactly expressed by the pro- 
duct of the weight of the air thus returned for use in 



132 COMBUSTION OF COAL. 

combustion into the actual temperature given it, and its 
specific heat. 

"The exact mode of estimating this was first indi- 
cated by Mr. J. S. Prideaux, and adopted by Rankine. 
According to results of experiments made with the mer- 
curial calorimeter — of course, under conditions unrealiz- 
able in practice — one pound of carbon, combined with 
its equivalent by weight, or two and two-third pounds 
of oxygen, will develop fourteen thousand five hundred 
British units of heat, or will raise fourteen thousand 
five hundred pounds of water one deg. Fahr, But, to 
effect the combination in the atmosphere, this amount 
of oxygen has to be taken in conjunction with the 
nitrogen of the air, amounting to nine and one-third 
pounds. In other words, the very least amount of 
atmospheric air used in combustion is twelve pounds; 
it is in many furnaces, especially those working with a 
chimney draught, required to be twice as much, or 
twenty-four pounds. Assuming the most probable case, 
that twenty-four pounds of air per one pound of carbon 
be taken, and that this carbon has been completely 
burnt, then, as atmospheric air consists of eight parts by 
weight of oxygen and twenty-eight of nitrogen, the 
products of combustion resulting from the one pound 
o£ carbon and the twenty-four pounds of air, weighing 
in all twenty-five pounds, will consist of three and two- 
third pounds of carbonic acid and twenty-one and one- 
third pounds of. inert, uselessly heated nitrogen. It is 
clear that, for instance, the more nitrogen there hap- 
pened to be mingled with oxygen, the greater the 



HEATED AIR AND CHEMICAL ACTION. 133 

weight of matter that would have to he uselessly raised 
in temperature ; aud that the greater its capacity for 
absorbing heat — the greater its specific heat — the greater 
the amount of heat that would be taken up. 

" We need scarcely observe that the so-called specific 
heat of any body is that amount of heat which it absorbs 
or gives out whenever its temperature rises or falls 
respectively; and the unit of measure in the scale of spe- 
cific heat is that of water. Thus, the specific heat of 
carbonic acid gas being 0.217 and of nitrogen 0.245, the 
mean of three and two-third pounds of the first and 
twenty-one and one-third pounds of the latter is 0.237 ; 
this, multiplied by the weight, twenty-five pounds, and 
divided into the fourteen thousand five hundred units of 
heat which can be generated from a pound of carbon, 
gives 2,440° as the temperature of the products of com- 
bustion, in the form of about one thousand eight hun- 
dred cubic feet of fire-gases. 

"From these figures alone is seen the paramount 
importance of thoroughly heating the air for com- 
bustion, of thoroughly heating its oxygen in order 
to facilitate combination with the carbon, and of pre- 
liminarily heating its nitrogen in order that its fourfold 
useless volume may not rob the heat required at the 
very moment and focus of combustion. E"ow, it is 
evident that the nearer the temperature of the useless 
nitrogen is raised to that of the fire, the less is the loss 
to the fire in unnecessarily heating it while it is parting 
with the oxygen; and whatever of this can be done by 



134 COMBUSTION OF COAL. 

means of the very escaping gases themselves is pure 
saving. 

"The very great difficulty in either heating or cool- 
ing air is its non-conducting capacity, or, more strictly 
speaking, the difficultity in obtaining a sufficiently 
rapid convection of heat to and from the mass of air 
employed. This is too well known to all contrivers of 
hot-air engines or of air-cooling machines; in cold cli- 
mates it constitutes the comfortable properties of flan- 
nels and furs. To heat or cool air, very extensive sur- 
faces, together with very great differences of tempera- 
ture, are hence absolutely necessary. We believe that 
the. Siemens regenerators are proportioned in such-wise 
as to give about seventeen pounds of fire-brick for each 
increment of gaseous fuels that can be developed from 
one pound of coal. As, however, only about one-fourth 
of the total regenerative capacity is being heated to the 
full temperature of the gases passing down through the 
ports, this amount has to be increased fourfold; so that 
nearly seventy pounds of fire-brick are probably used 
per pound of product of combustion. The surface of a 
Ponsard recuperator for an ordinary re-heating furnace 
is stated to average twenty-three square metres, half of 
which is for cooling the fire-gases, and the other half 
for heating the air; and therein the air is stated to 
attain the temperature of 1,500° Fahr. When, as in 
the Boetius furnace, the sides or the top or bottom of 
the furnace are used to heat the air, the air is, firstly, 
not merely heated, but, secondly, jit serves as a cooling 



HEATED AIR AND CHEMICAL ACTION. 135 

medium — protecting the brickwork by keeping down 
the temperature. The heat, also, that would otherwise 
be uselessly radiated is thus picked up by the air during 
its circulation, actual trials with the pyrometer having 
shown that the air can be heated in this way up to 600° 
Fahr." 



CHAPTER VII. 

THE FURNACE. 

Furnace Draft — Sectional Area of Chimneys — Height of Chimneys 
— Volume of Escaping Gases — Weight of Escaping Gases — Tem- 
perature of Escaping Gases — Distribution of Air in the Fur- 
nace — Admission of Air Over the Fire — C. Wye. Williams 
Plan — T. S. Prideaux' Plan — W. A. Martin's Plan— Experi- 
mental Test of the Martin-Ashcroft Furnace Door at U. S. 
Navy Yard, Washington — Perforated Pipes — Admission of Air 
at the Bridge-Wall — R. K. McMurray's Plan for Admitting 
Heated Air — Admission of Air and Evaporation. 

Furnace Draft may be produced by any one of the 
following methods : 

1. A natural chimney draft, or that due to the 
unbalanced pressure of a column of heated gases. This 
may be modified; 

2. By the use of a jet of steam escaping into the 
chimney through a contracted orifice, by which an 
increased draft is obtained over that given above ; this 
may be either " live " steam from the boiler or the 
exhaust from a non-condensing engine. 

3. By a forced draft produced by a fan-blower, or 
other device. 

The first is almost exclusively employed in con- 
nection with stationary steam boilers. The object of 
chimney draft is to supply oxygen to the burning fuel, 
and then, to get rid of the products of combustion. 

The sectional areas of chimneys usually bear some 
empirical relation to the area of the grate. In practice 



FURNACE DRAFT. 137 



this sectional area varies from one-sixth to one-tenth of 
the grate. After a series of elaborate experiments Mr. 
Isherwoocl fixed upon one-eighth of the area of the 
grate as being the best proportion for draft area, and 
which will be near enough for the area of chimneys in 
any ordinary practice. 

The height of the chimney is often determined by 
the character of the surroundings, such as buildings, 
hills, etc., and in cities, the minimum height is not unfre- 
quently fixed by local legislation ; but aside from this, 
there is a great deal of "rule of thumb" about it. The 
building of a chimney costing, say from two thousand 
to five thousand dollars, is designed not only for pres- 
ent, but for prospective future needs, and the desire is, 
that it shall be amply large for an uncertain future 
requirement. 

Within reasonable limits there is no objection to a 
large, and especially a high chimney — other things being 
equal — the higher the chimney the better the draft. 

Furnace draft is caused by the difference in weight 
or pressure of the column of cold air outside of the 
chimney, and the weight of the column of heated gases 
within it. Air and gases, when heated, expand in 
volume, and become less dense than for equal volumes 
at a lower temperature ; this difference in density is the 
draft-producing quality of heated gases. The increase 
in volume, for different temperatures, has been calcu- 
lated by Professor Rankine. The following are some of 
the results : 



138 



COMBUSTION OF COAL. 



Table XVII. 

Showing the Volume of Escaping Gases in Cubic Feet per Pound 
of Coal Burned. 





POUNDS 


OF AIR PER POUND OF COAL. 












12 POUNDS. 


18 POUNDS. 


24 POUNDS. 


FAHR. 


CUBIC FEET. 


CUBIC FEET. 


CUBIC FEET. 


32° 


150 


225 


300 


68 


161 


241 


322 


104 


172 


258 


344 


212 


205 


307 


409 


392 


259 


389 


519 


572 


314 


471 


628 


752 


369 


553 


738 


1112 


479 


718 


957 


1472 


588 


882 


1176 


1832 


697 


1046 


1395 


2500 


906 


1359 


1812 



From the above table it will be seen that if 225 
cubic feet of air, at a temperature of 32° are necessary 
for combustion, it will require 241 cubic feet, if supplied 
at 68° * 

Supposing 241 cubic feet of air at a temperature of 
68° are supplied to the furnace per pound of coal burned 
per hour, the volume of escaping gases will be increased 
when discharged into the chimney to 471 cubic feet, if 
the temperature of the escaping gases is 572°. 

*It will be a near enough approximation in this case to assume that the products 
of combustion ami air will, at the same temperature, occupy similar volumes. 



FURNACE DRAFT. 139 



The weight of escaping gases will equal the weight 
of the air and the combustible portion of the fuel. At 
two hundred and twenty-five cubic feet, as above, there 
are required eighteen pounds of air to one pound of 
combustible ; the increase in volume from two hundred 
and twenty-five, to two hundred and forty-one cubic feet 
does not change the weight of the air, but the four 
hundred and seventy-one cubic feet of gases, instead 
of weighing eighteen pounds, will weigh 18 + 1 = 19 
pounds. 

We can then suppose two columns, one of air at a 
temperature of 68° weighing eighteen pounds and 
occupying two hundred and forty-one cubic feet, and 
one of gases, at a temperature of 572°, weighing nine- 
teen pounds, and occupying four hundred and seventy- 
one cubic feet. The lighter gases being confined to the 
chimney, rise to the top by virtue of their lesser gravity; 
the higher the chimney, and the higher the temperature 
of the escaping gases, the stronger or more intense will 
be the draft. 

In height, chimneys usually vary from forty to one 
hundred and twenty feet: it is seldom that the latter 
figure is exceeded, and when it is, it is generally for 
other reasons than for draft simply. A table prepared 
by Mr. Theron Skeel, gives the relative amount of coal 
that can be burned in the same time, with chimneys of 
various heights, as follows : 

Height of chimney, in feet 120 100 80 60 40 20 

Kelative amount of coal 100 90 80 70 57 40 



140 COMBUSTION OF COAL. 

After a moderate height of chimney is reached, the 
effect of any increased height is very small. It rarely 
occurs that a height of more than one hundred feet is 
needed for draft even when permanent chimneys are to 
be built. When iron chimneys are employed the 
heights commonly vary between forty and seventy-live 
feet. 

Knowing the rate of combustion, and the area of 
the chimney, the following rule of Boulton and Watt 
for determining the height of the chimney is a good 
one, taking into account all the uncertainties attending 
chimney proportions : 

Rule — Multiply the number of pounds of coal con- 
sumed under the boiler per hour by twelve, and divide 
the product by the sectional area of the chimney in 
square inches ; square the quotient thus obtained, which 
will give the proper height of the chimney in feet. 

This very closely approximates Peclet's formula, so 
elaborately presented by Professor Rankine in his treat- 
ise on the steam engine, and to which the reader is 
referred for the mathematics of chimney proportions; 
also, Weisbach's Mechanics — DuBois — vol. 2, part 2 ; 
or Trowbridge's Heat and Heat Engines. 

The connection between the boiler and chimney 
should be as short and direct as the circumstances will 
permit. The area of the chimney should be one-eighth 
of the grate. The grate should be of such size as to burn 
all the combustible matter without loss, and without 
forcing the fire beyond the point of economic combus- 
tion. 



DISTRIBUTION OF AIR IN THE FURNACE. 141 

The best temperature for the escaping gases is held 
in practice to be nearly, but not quite, that sufficient 
to melt lead, that is, a temperature a little below 600° 
Fahr. 

It is especially worthy of remark, that a moderate 
force of draft through the fuel seems to be the condition 
which is best suited to the fullest economical perform- 
ance, speed and power both considered, of the semi- 
bituminous and bituminous coals, while to the anthra- 
cites a strong current is best adapted for the same ends. 

The maximum heating effect from any coal is pro- 
cured when the air passes through it fast enough to burn 
entirely all the combustible matter it can surrender to it 
by its own heat; but when the current exceeds this rate, 
its influence is counteractive, cooling and quenching a 
portion of the burning matter, and driving it waste- 
fully forward, with the combustion not completed. The 
different ignitibility of the various classes of fuel sets, 
of course, different limits to this point of economical 
rapidity of blast and of combustion — limits which are 
sooner passed with the bituminous than with the 
anthracite coals. 

Distribution of Air in the Furnace — Air, when admitted 
through the ash-pit, and coming in contact with a mass 
of incandescent coke or anthracite coal on the grate, 
yields up its oxygen and combines with the carbon of 
the fuel; first, in the proportion to form carbonic acid 
(CO,), then, in passing through this bed of ignited fuel 
takes up another equivalent of carbon, and converts the 
carbonic acid (CO*) into carbonic oxide (CO). 



142 COMBUSTION OF COAL. 

Supposing the heat units of the net combustible, 
when burned to carbonic acid, to be, say, 14,000 ; if 
burned to carbonic oxide, the heat units would amount 
to, about, 4000, showing a difference of, say, 10,000 heat 
units per pound of net combustible, or more than sev- 
enty per cent, of loss, perhaps waste would be a better 
word, for air costs nothing, and oxygen is all that is 
needed to effect the saving. 

The distribution of air above and below the lire is 
intended to counteract this loss, by supplying air under 
the grate to burn the fixed carbon or coke, and above 
it, to supply the oxygen needed to re-convert this car- 
bonic oxide into carbonic acid. 

In the burning of a coal rich in hydrocarbons smoke 
is produced in large quantities, and if these particles of 
solid carbon are mixed with carbonic acid gas while 
still in the furnace and at a high temperature, they dis- 
appear as smoke, and convert the carbonic acid already 
formed in the furnace into carbonic oxide, by yielding 
up their carbon to the heated gas; most, if not all of 
which, might have been prevented by slow combustion, 
and a proper supply of air above the fuel. 

The quantity of air to be admitted above the fire 
and the best relative position for its admission, is a 
matter of furnace detail to be determined and fixed by 
experiment, rather than one pertaining to the theory of 
combustion. It is one of great importance, however, 
and is entitled to more consideration than it generally 
receives. 



THE PRIDEAUX FURNACE DOOR. 143 

C. WYE. WILLIAMS' FURNACE DOOR. 

Mr. Williams has given this subject a great deal of 
attention, and recommends a tire-door consisting of two 
plates; the door proper, with an opening through it, 
and another plate as near the size of the fire-door open- 
ing as possible and allow the door to be closed; this 
plate may be from two to three inches back of the fire- 
door plate, and. should contain as many perforations 
about -4- inch diameter as will make the asrffreffate 
area of these perforations -^- of the grate surface. 

The air may be admitted through the fire-door into 
the furnace at a constant rate, or, the flow of air may be 
checked by the closing of a "butterfly" register on the 
outside of the door. This fire-door has worked well in 
practice, especially with anthracite coal. 

THE PRIDEAUX FURNACE DOOR. 

Invented by Mr. Thomas S. Prideaux, England, is 
represented in plate I, and is thus described in the speci- 
fication of his American patent : 

" This invention relates to apparatus for regulating 
the supply of air to furnaces in such a manner as to 
afford the furnace an additional supply of air after coal- 
ing, which supply shall gradually diminish and eventu- 
ally cease after a certain definite period of time by the 
action of an automatic apparatus, thus securing the cut- 
ting off of the additional supply of air, when no longer 
required, independently of the attention of the fireman. 

" The apparatus consists of two parts : First, a case 
or air-chamber in the exterior of the furnace, furnished 



144 COMBUSTION OF COAL. 

with a flap or cover moving on an axle, so as to admit 
or exclude the air at pleasure, and communicating with 
the interior of the furnace through the fire-door and 
two channels placed laterally, the exit-mouths of these 
passages being furnished with grating suitable for heat- 
ing and distributing the air as it passes into the furnace, 
and at the same time preventing the radiation of heat out- 
ward, while the throat of the air-chamber is furnished 
with a damper moving on an axle, which, according to 
the angle its surface makes with the axis of the line of 
draft, interposes a greater or less impediment to the 
influx of air, thus affording the means of varying the 
quantity of the supply according to the character of 
the fuel and the urgency of the firing. Secondly, a 
motor-regulator, by which the gradual closing of the 
lid of the air-chamber is automatically effected. This 
motor-regulator consists of, first, a cylindrical cup or 
cistern pierced with a small orifice at the bottom and 
having a rod rising from its center: secondly, a cast- 
iron cylinder, about one and a half times the depth of 
the cistern, and sufficiently larger in diameter to admit 
of the cistern traversing freely within it when the appa- 
ratus is charged with mercury, and having a cylindrical 
block or plunger attached to the under side of the cover, 
pierced in the center for the passage of the cistern-rod, 
which plunger is to be of a diameter as much less than 
the interior of the cistern as will allow of the free pass- 
age of the mercury, thus enabling the cistern to be rap- 
idly raised to the top of the cylinder. 



THE PRIDEAUX FURNACE DOOR. 145 

"The manner in which my said invention is host car- 
ried into practice may be fully understood by the aid of 
the accompanying drawing, which I will now proceed to 
describe. 

"Figure 1 shows a front elevation of an apparatus to 
be applied to the mouth of a furnace, and constructed 
according to my invention. Figure 2 is a cross-section 
of the same through the line A B. Figure 3 is an end 
elevation. Figure 4 is a longitudinal section through 
the line C D. Figure 5 is a horizontal section through 
the line E F, and Figure 6 is a back elevation of the 
said apparatus. Figures 7, 8, 9 and 10 are hereinafter 
described. 

"The apparatus works as follows: The charge of 
mercury is placed in the cistern at the bottom of the 
cylinder, and the cylinder-cover screwed down. Upon 
the cistern being raised to the top of the cylinder the 
plunger enters the cistern, displacing the mercury and 
causing it to flow over its sides and pass down the 
circumferential interstice to the bottom of the cylinder. 
The raising of the cistern is effected by the lifting of 
the lid of the air-chamber, while the weight of the 
latter, slightly depressing the cistern, causes the mercury 
to rise in the circumferential interstice between the 
cylinder and the cistern to a height considerably above 
the level of the bottom of the cistern. The mercury, as 
a consequence, flows into the cistern through the small 
orifice in a time proportionate to the size of the orifice, 
the amount of the charge of mercury, and the force of 
gravity exerted by the suspended weight. 
(11) 



146 COMBUSTION OF COAL. 

"To prevent the access of dust or steam to the 
interior of the motor-regulator, I construct a closed 
channel, I, on each side of the exterior of the cylinder, 
extending throughout its length, for the passage of the 
side rods s from the cross-head A*, the cross-head itself 
being covered with a hood or cup, o, the lower edge of 
which is in apposition with the upper faces of the 
lateral channels, by which the access of dust or steam is 
effectually prevented. 

"An alternative plan for excluding the entrance of 
dust or steam, compact and elegant in appearance, but 
entailing slightly more friction and requiring greater 
delicacy and accuracy in workmanship, is to construct 
the cistern-rod / hollow, so as to enable it to contain 
within it, and travel freely upon, a small tube, u, securely 
tapped into the bottom of the cylinder, 

" This tube must be of such a size as to allow of the 
traverse within it of a small rod, r 7 which may be 
termed the connecting-rod, attached at its upper end to 
the top of the cistern rod (or rather tube) by a pin- 
joint, i, and at its lower to the lid of the air-chamber by 
a short link. 

"To enable the motor- regulator to sustain a heavier 
weight, thus lessening its liability to derangement by 
friction, and at the same time affording within certain 
limits the means of varying the time occupied in its 
descent, I apportion the depth of the plunger h, cistern 
d,'a,n& cylinder g, so that the edge of the cistern con- 
siderably overlaps the bottom of the plunger. As the 
velocity with which the quicksilver traverses through 



THE PRIDEAUX FURNACE DOOR. 147," 

the orifice and enters the cistern increases with the pres- 
sure, the wider the range of pressure available the- 
greater the power of varying at pleasure, by means of 
movable weights, the time of the descent and the closure 
of the air-valve. 

"To prevent the interior of the motor-regulator' 
becoming rusty, thus giving rise to a friction which, 
impairs its action, I heat it in detached pieces to a tem- 
perature of about 600° or 700°, and then plunge it into^ 
warm linseed-oil, after which it is carefully wiped and. 
then thoroughly washed with benzoline. 

u a shows the exterior air-case divided into three 
chambers or passages, b, the cover or damper connected; 
by a link to the connecting-rod attached to the cistern- 
rod of the motor-regulator or cylinder g. The cover 
or damper b of the air-chamber may be opened 
by the fireman when he closes the door after 
coaling, but I prefer to make it self-opening by the 
aid of the segment of a screw, y, formed on the 
hinge of the furnace-door, which raises a lifting-bar, 
;?, upon the door being opened, c is the grating for 
heating and finely dividing the air on its passage into 
the furnace, and at the same time assisting in conjunc- 
tion with the plates of sheet-iron t (having vertical slits 
or openings so placed that the intervals shall not corres- 
pond), to prevent the passage of the radiant heat out- 
ward, p is the flap, the office of which is to vary the size 
of the neck of the air-chamber. w f is a movable weight 
suspended from the tip of the link, which attaches the 



143 COMBUSTION OF COAL. 

connecting rod to the cover of the air-chamber, and 
which is furnished with a small hole for the purpose. 

"Figure 7 shows a vertical section of the motor-reg- 
ulator with a hollow cistern -rod. Figure 8 is a horizon- 
tal section of the same, g is the cylinder ; d, the cup or 
cistern, h is the plunger, which displaces the mercury, 
and causes it to now over the rim of the cistern into the 
cylinder when the cover of the air-chamber is raised. 
/ is the hollow cistern-rod; e, the orifice for the passage 
of the mercury; u, the tube tapped into the bottom of 
the cylinder; w, a weight, advantageously placed to 
assist by its gravity in overcoming any friction opposing 
the closing of the apparatus; o, the hood or cap for 
excluding dust and steam, m is the connecting-rod, 
and i its pin-joint. Figure 9 shows a vertical section of 
the motor-regulator, with a cross-head and closed chan- 
nels for the passage of the side-rods. Figure 10 is a 
view of the same, seen from above, showing the hood or 
cap, and the channels for the passage of the side-rods. 
g is the cylinder; d y the cup or cistern; A, the plunger; 
/, the cistern-rod ; e, the orifice for the passage of the 
mercury; o, the hood or cap for excluding dust and 
steam; k, the cross-head; s, the side-rods, and I the 
channel for the passage of the side-rods." 

THE MARTIN FURNACE DOOR. 

The furnace-door, of which Figure 2 is a sectional 
representation, is the invention of Mr. W. A. Martin, of 
England, and is now being introduced in this country 
by the Ashcroft Manufacturing Company, Boston, Mass. 



T. S.FRIDEAUX. 
APPARATUS FOR REGULATING THE SUPPLY OF All 

TO FURNACES. 



F/G.Z 



FIG.2> 




HcurjnersteuiBrvs & Co.Zrih-Jndia^apolis.Irui. 



THE MARTIN FURNACE DOOR. 



149 



This door consists in the combination of a furnace door, 
pivoted on a horizontal axis, at, or near, its upper edge, 
and made to open and close by being swung pendulum- 
like through the lower arc of a circle, and a count erbal- 
ancing-weight for retaining the door in the desired 
position. 




Figure 2. 

By opening this door a few inches inwardly the air 
is caused to enter and pass among the fuel, and to min- 
gle with the gases proceeding therefrom in the process 
of combustion after they rise from the fuel, thus causing 
them to unite and to be consumed before leaving the 
furnace, instead of leaving it in the condition of smoke, 
or unburned gases; and by opening it outwardly to the 
required extent, ample provision is made for the inser- 
tion of the fuel. 



150 



COMBUSTION OF COAL. 



Experiments were made at the Washington Navy 
Yard, in 1874-5, to determine the relative economy of 
this furnace-door, over the ordinary door, the latter 
being that recommended by C. Wye. Williams, and 
described on page 143. 




Figure 3. 

Figure 3 is a representation of a front view of the 
boiler, as fitted with the experimental door, and the 
following table gives the comparative results: 



THE MARTIN FURNACE BOOK. 



151 



? -«! 

s « 

x ° 

Ed O 

ft -: 

X § 

— I s 

o 3 

3q g 






H 


S 


g 


>: 


U 






p; 


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fc 


H 


■«! 



X 



5 O 



■< 



r ft 



^ id 
































cc 








X t> 


o « 2 










co oi -••-. 




2* 


o« 


O 33 


r— 


cc 




| 


3! M 

a a 
a- Q 




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cc 


o 


CO »H 1-1 t J 


"s 


x « 


-« * 












£ 


as 


<; 












2 


00 


£ 8 

O ~ t 
« o « 


b 

O* ~> OH -i -* = CO ^ c. 11 


© 


\^IC"? O l^O_L £ 


fc 


l> IQ IfS 


1 00 CO ^ 


— zt -s 


V 


i-l O £ O — ^ Ai CN 


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m 




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N g, bJ £> g> _• cn os -• _ 


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l- CT. CO I 


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a 


w O C 


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rt '^ 








































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: 3 — 






































3 & 


: % v 






1 






























^ 


c5 S 


- ^ s 






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3 


"g ' c 


: ?• 8 






s 






























93 


c 


: - o 






















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a; 


3 iC 


: ° i? 






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w 












s, 


« 'g 


2 i 






£ 
















| 












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CJ 


t 'Sb 


— o 

c3 2 






o 
















co 














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o -2 


































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X 
















S q 






















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bn 












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= M i 


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B 


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5 




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cq 




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p 






"" ^ , CO 

u. ^3 TS .-. 

o ^ 4» g 
g 5 S o 

= 2 a,- 


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2 C 


3C 

o 




D 




1° 8 * 




-i 






a. 






& d 
9 ts 




£■ 






C 

a 
c 


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a 

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t- 
a 

c 

- 
c 

' r 
u- 

c 
c 

a 

e 
c 
£- 


c 

6 

s 

T 
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C 

-5 

p 
— 


Ik 

e 

c 

c 


c 

i 
z 

■r 
S 

■c 

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c 


c 
b 

b 



a 

c 
a, 

a 

:~ 
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j. 

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) £ 


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1 
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C 


a 

c- 

tt 

01 

I 

e 


1 .s 

■— u 

5 a 

rt ? 
cT £ 

% = 

C to 


PouiuLs of water that could have hern eva 
pressure by heat required from the fu€ 


+= CB 

09 3 

Is 
si: 

2 „ = 

ll 


CN 

C 

E 3 
c 

'J 

c 

p. 

a 


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cc 

= 

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51 

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* 



152 COMBUSTION OF COAL, 

The boiler with which these experiments were made 
is of the cylindrical, horizontal, tubular type, seventeen 
feet eight inches long, six feet in diameter, containing 
one hundred and fifty-seven brass tubes, ten feet long, 
and two and one-fourth inches outside diameter; having 
two furnaces, with a combined grate-surface of twenty- 
two square feet; and a heating-surface of nine hundred 
and twenty-eight square feet. 

The doors have an opening of one hundred and 
eighty-six square inches each, and are constructed in the 
usual manner, with an outer shell of cast-iron, contain- 
ing seven one and one-fourth inch holes," and with an 
inner plate of wrought iron with a space between them 
of three inches, the inner plate being perforated with 
small, holes through which the air is distributed over 
the fuel. 

Perforated Pipes— Instead of admitting the air 
through the furnace door, as described in the preceding 
pages, it is sometimes admitted through the sides of the 
furnace above the fuel, and sometimes back of the 
bridge-wall; perhaps the device most frequently used 
for this purpose is a cast-iron pipe, about six inches in 
diameter, and perforated with small holes; the deter- 
mining of the aggregate area of these perforations does 
not seem to rest upon anything in particular, and is 
almost entirely a matter of caprice; this pipe extends 
into, or through, the combustion chamber under the 
boiler, and is built into the walls, the ends of the pipe 
being left open to the air. "Whenever a device of this 
kind is employed it should never be far removed from 



ADMISSION OF AIR AT THE BRIDGE-WALL. 153 

the bridge-wall, and it is, at best, of doubtful utility if, 
by this means, an excess of cold air is allowed to pass 
into the chamber back of the bridge-wall ; for it should 
be remembered that oxygen alone is not what is needed, 
but a high temperature also, to insure the ignition of 
the carbonic oxide, which is the only reason for its 
admission at all. 

Admission of Air at the Bridge-wall — The admission 
of air at this particular point is intended to supply the 
oxygen needed to complete combustion in case it should 
be imperfect, while the gases are still at a high tempera- 
ture. A very successful device for the admission of 
heated air, near the point of the generation of gases in 
the furnace, was patented by Mr. R. K. McMurray, 
Xew York City, and is shown in plate II. 

"The improvement consists in combining with the 
furnace and combustion chamber a hollow cast-iron 
fire-bridge, formed of a series of plates united together 
and resting on the top of a bridge-wall of the ordinary 
construction, without being imbedded therein, into 
which hollow bridge fresh air for supply to the combus- 
tion chamber is introduced, and within which it is 
heated to a temperature approximating to that of the 
gases escaping from the furnace, and is thence delivered, 
in a minutely divided condition, to the gases as they 
enter the combustion chamber. The improvement fur- 
ther consists in such construction of the fire-bridge as to 
provide ample resistance against blows or shocks, and 
the effects of expansion and contraction, as well as to 
render it capable of being readily and quickly removed 



154 COMBUSTION OF COAL. 

from its position in the setting, renewed or repaired at 
a comparatively slight expense, and replaced in position 
for further operation. 

" The construction of the lire-bridge and its applica- 
tion in the setting of a return tubular stationary boiler, 
are clearly shown in the accompanying illustration. It 
consists of a lire-plate A, a back or base-plate B, and a 
dispersing-plate C. The plate A is corrugated in order to 
give it increased strength, and allow for expansion and 
contraction under change of temperature, and is pro- 
vided with a light-bottom flange, which rests upon the 
bridge-wall, and thence rises vertically for about two- 
thirds of its height, at which point it is inclined at an 
angle of about forty-five degrees. The bottom plate B 
conforms in the relative position of three of its sides to 
the plate A, and terminates below in a horizontal foot. 
The plates A and B are connected by bolts passing 
through thimbles, so as to form a hollow case. The 
perforated diffusing-plate Cis inserted in grooves formed 
in the other plates. A series of air-supply openings D 
are formed in the plate B, near the base ; above them 
extends a deflecting flange, E. The bridge so set that 
the lower edge of the lire-plate A is slightly below the 
level of the grate-bars, and its ends are closed by the 
side walls of the setting, or by metal plates fitted 
therein; the latter arrangement allowing of the bridge 
being removed when desired by drawing it out longi- 
tudinally through the opening in the side wall. 

"The fresh air enters the space between the back 
plate and the fire plate through the supply openings D 



m'murray's bridge-wall. 155 

and is deflected by the flange against the heated surface 
of the fire-plate, and thence passes upward, as indicated 
by the arrows, figure 2, along the space between the 
two plates. The air is thus introduced in a minutely 
divided condition into the combustion chamber at a 
temperature closely approximating that of the gases 
escaping from the furnace. It mingles with these gases 
and oxidizes the carbonic oxide, effecting complete com- 
bustion with a corresponding economy of fuel and pre- 
vention of smoke. 

"In applying the bridge in a setting it is placed upon 
the top of the usual brick bridge, the lower edge of the 
lire-plate A being slightly below the top of the grate- 
bars. It can be removed whenever necessary by being 
drawn out longitudinally through an opening in the side 
wall, without disturbing any of the brick work of the 
bridge on which it rests, or any other part of the setting, 
and replaced in a similar manner. This can be done in 
a very short time, and without the necessity of awaiting 
the cooling down of the furnace and combustion cham- 
ber. The capability of ready removal and replacement 
for renewal or repair constitutes an important and 
valuable feature of the improvement as. compared with 
the ordinary brick bridge-walls, or with devices imbed- 
ded therein, or in the setting. 

"Its advantage, moreover, in durability will be appar- 
ent to the practical engineer and steam user, inasmuch 
as the fire-plate only is exposed to the direct action of 
the fire ; and, from its material and form of construction, 
is possessed of greater pow T er of resistance to the des- 



156 COMBUSTION OF COAL. 

tractive influences exerted upon it. In the event of 
repair the entire bridge can be removed, a new fire-plate 
be inserted, and the bridge replaced in position, with 
much less labor and expense, and with far greater expe- 
dition, than is practicable in the case of a brick bridge- 
wall. 

"The bridge is adaptable to any shape or size of 
furnace used in conjunction with steam boilers, re-heat- 
ing furnaces, blast furnaces, and tan-bark ovens, without 
change in the brick work or setting, other than remov- 
ing the upper portion of the brick bridge-wall, and 
forming an opening in the side wall for the insertion of 
the bridge." 

This bridge-wall has been adopted by the Hartford 
Steam Boiler Inspection and Insurance Company, in 
their system of boiler settings, and is said by them to 
give good results in practice. 

The admission of air above or beyond the fuel is not 
alway s to be regarded as a remedy for the low evapora- 
tive efficiency of a boiler or the low heating power of 
coal under all conditions. Sometimes this admission of 
air may prove to be of the greatest value ; under other 
conditions, it may not be of the slightest service, and, 
indeed, it may lower the temperature of the furnace so 
far below the point of economy as to prove an evil 
instead of a remedy. 

Unfortunately there is no way in which this question 
can be finally settled, except by direct experiment, and 
this would apply to one particular furnace only, and 
perhaps for only one particular kind of coal, i. e., either 



Fiq. 2 




McMURRAY'S CORRUGATED IRON AIR BRIDGE WALL. 



EQUIVALENT EVAPORATION. 157 

anthracite or bituminous, but not both. As the subject 
now stands, it amounts to little less than a mere specu- 
lation to predict in advance the performance of any 
furnace, in so far as perfect combustion is concerned, 
but in general terms it may be said that, if the perform- 
ance of any boiler has an equivalent evaporation of less 
than ten pounds of water, from and at a temperature of 
212° Fahr. per pound of net combustible, there must 
certainly be something wrong in the construction of the 
boiler, furnace, or setting, which demands immediate 
attention. 



CHAPTER VIII. 

PRODUCTS OF COMBUSTION. 

Carbonic A cid — Carbonic Oxide — Water — Nitrogen — Sulphurous 
Oxide — Surplus Air — Smoke— Products of Perfect Combustion 
Invisible — How Soot is Formed — Smoke-preventives — The Cor- 
rosive Action of Sulphur on Boilers — Ashes and Clinker — 
Analysis of Coal Ashes — Color of Ashes as Indicating the Pres- 
ence of Iron Pyrites in Coal — The Formation of Clinkers — The 
Influence of Iron in the Coal on the Formation of Clinker — 
Apparatus for Gas Analysis. 

The combustible elements in coal are carbon, hydro- 
gen, and sulphur, the atmosphere furnishing the oxygen 
necessary to convert the carbon into one of the two 
following products : 

FORMULA. COMBUSTION. PRODUCT. 

Carbonic acid, CO^ complete, incombustible. 

Carbonic oxide CO incomplete, combustible. 

The hydrogen unites with oxygen to form water 
EL, 0, in which the combustion is complete, and the pro- 
duct incombustible. 

The nitrogen of the air remaining in the furnace after 
the union of the oxygen with the carbon and hydrogen, 
is incombustible, and acts as a dilutant of the gases in the 
furnace, having no affinity for any of the products of 
combustion. 

The sulphur combines with oxygen to form sulphur- 
ous oxide SO.,, a colorless gas, with a suffocating odor; it 
is a non-supporter of combustion, instantly extinguish- 



SMOKE. 159 



ing flame when "brought within its influence. Sulphur- 
ous oxide, in absorbing the vapor of water, changes 
from 

Sulphurous oxide, S0 2 to 
Sulphurous acid, SO 2 , H 2 

As there is almost always an excess of air supplied 
the furnace, often amounting to twice the quantity 
needed for combustion, this excess, also, becomes waste 
product, and acts as a dilutant of the furnace gases. 

Smoke is regarded as a product of incomplete com- 
bustion. In its widest application it is made to include 
all the products of combustion issuing from the chim- 
ney. The use of the word is here restricted to the par- 
ticles of solid carbon mingled with the escaping gases, 
or, it is the sooty portion only, of the escaping products. 
If the combustion of coal was perfect the escaping gases 
would be invisible. Very few analyses of smoke are on 
record, but our knowledge of the composition of coal, 
and of the products of the chemical union of oxygen 
with its several constituents, we may easily conjecture a 
qualitative composition of the escaping gases, though 
the precise quantities of each may be unknown. 

When a charge of bituminous coal is thrown upon 
the fire, the effect of the heat is to detach small parti- 
cles of coal from the surfaces most rapidly heated ; these 
particles are generally very small, and in consequence 
weigh so little as to be easily carried over the fire and 
up the chimney by the mechanical agency of the draft 
alone. These particles of solid carbon reflect light, and 



160 COMBUSTION OF COAL. 

it is this property which renders them visible. If these 
particles of carbon were not present, the remaining 
products would be invisible. "Whatever the quantity of 
coloring matter in the smoke as seen escaping from the 
chimney, it is to be regarded as so much fuel irrecover- 
ably lost. The solid carbon passing off in this manner 
is often a considerable quantity, but the actual percent- 
age is almost always overstated. Sometimes furnaces 
are so badly constructed that the chimneys leading from 
them are almost constantly pouring into the atmosphere 
a volume of gases, which, to judge from appearances 
merely, would seem to be half carbon, or, that half the 
coal fed into the furnace was passing off un combined. 

This mistaken notion as to the percentage of carbon 
present, has been so generally overrated, that devices 
for " burning smoke " have been offered by the score, 
often accompanied by the most absurd claims in regard 
to their efficiency as a " smoke consumer," and the great 
saving in coal to be effected in the event of their 
adoption. 

What is needed is not so much a smoke consuming 
as a smoke preventing furnace, one which shall be so 
designed that any fuel rich in hydrocarbon, can be com- 
pletely burned in the furnace proper, or within the 
chamber containing the incandescent fuel. This can be 
done only, by the admission of sufficient air to convert 
the carbon into carbonic acid and still maintain a 
high temperature in the furnace. The quantity of air 
required in the combustion chamber of a furnace is 
greater when a fresh charge of bituminous coal is thrown 



SMOKE. 161 



upon the fire, than that needed a few minutes afterwards. 
If the high temperature of the furnace could be main- 
tained at the same time a fresh charge is thrown upon 
the fire, the carbonic acid would entirely dissolve all: 
the sooty carbon present in the flame and convert itself 
by this additional carbon into carbonic oxide, which may 
then by a proper supply of air be re-converted into car- 
bonic acid by the addition of another equivalent of 
oxygen. 

t/ CD 

Smoke-prevention in a badly constructed furnace is- 
attended with great practical difficulties; the chief one 
is the admission of cold air over the fire in a sufficient 
quantity to convert these minute particles of carbon 
into carbonic acid, and at the same time not lower the 
temperature of the furnace so as to affect the steam- 
producing power of the boiler, per pound of coal. In 
admitting air above the fuel, unless it can be supplied 
hot, it may prove a worse evil than the smoke itself, by 
lowering the temperature of the gases in the furnace to 
a point below which ignition is insured. In stationary 
boiler furnaces, in which much smoke is given off, per- 
haps the best thing to do is to lengthen the grate by 
carrying the bridge-wall farther back ; the limit to this 
extension is a six-foot grate; in this manner increased 
grate area is obtained, and a slower rate of combus- 
tion. Now, by proper firing, this may be a means of 
largely reducing the escape of soot and carbon. The 
coal should not be spread evenly over the grate, but 
banked up near the door, and allowed to distill off the 

gaseous portions slowly, which, in passing over the bed 
(12) 



162 COMBUSTION OF COAL. 

of incandescent fuel, are burned; after the charge of 
fuel has lost most of its volatile matter it may then be 
broken up and spread over the grate. 

A fire-door, having perforations, or preferably au air 
inlet along its lower edge only, may prove of great ser- 
vice in admitting air where it is most needed. 

In cases where the above is not practicable, a fan- 
blast may be used in connection with a closed ash-pit, 
and thus greatly intensify the action of the furnace; in 
which case the grate area may be reduced. 

By either of these methods the quantity of smoke 
escaping may be reduced to within very narrow limits, 
if not entirely prevented; the latter, however, can 
scarcely be expected so long as coal is fed to the furnace 
in large lumps, and in considerable quantities, at long 
intervals. 

SULPHUR A CAUSE OF CORROSION IN BOILERS. 

There exists in France a commission whose special 
duty it is to look after boilers, and to try and find out 
the causes of accidents. A report was made to this com- 
mission after a thorough examination by M. Hanet- 
Clery, a mining engineer-in-chief, on the corrosion of 
steam boilers by the action of sulphuric acid. The com- 
mission had its attention drawn to the explosion of two 
steam boilers, one at a colliery in the Nievre, the. other 
at the Ougree iron works, in Belgium, and which were 
attributed to the destructive effect on the metal in con- 
sequence of the presence of sulphuric acid in deposits 
left b} T the smoke on certain parts of the sides of the 



SULPHUR A CAUSE OF CORROSION IN BOILERS. 163 

boiler. Other facts, or supposed facts, of like import 
appeared, and the subject was brought before the scien- 
tific and industrial world in the Annales des Mines et des 
Ponts et Chaussees, the problem being whether, under 
given conditions, the sulphurous acid of the smoke was 
turned into sulphuric acid, and the report of M. Hanet- 
Clery is one of the results (25). 

"As regards the two accidents already referred to: 
• "1. The one which happened at the colliery oc- 
curred under the following circumstances : The boiler 
which burst was cylindrical, the fire being placed exactly 
beneath, and a superheater, from the cylindrical boiler 
by a brick arch, which nearly touched the upper part of 
the superheater. The latter was torn wide open in 
front, to the right of the strip which covered a longi- 
tudinal joint of two plates of iron, and then perpendic- 
ularly to the end on both sides. 

" The thickness of the iron at the part which gave 
way first had originally been twelve millimeters, or half 
an inch nearly, but it had been reduced to 1.7 millime- 
ter, and consequently totally incapable of supporting 
the pressure of six kilograms, under which the boiler 
worked. The destruction of the iron was all on the 
exterior, and extended — though not equally — over the 
upper end on the side not exposed. The mischief had 
all occurred in five years. 

" M. Douville, a mining engineer, attributed it to the 
corrosive action of oxygen and sulphurous acid, con- 
tained in the products of combustion in the presence of 
water coming from a fissure in the boiler above, which, 



164 COMBUSTION OF COAL. 

having traversed the brick vaulting, fell on the re-heater ? 
wetting the upper part, which was relatively cold, being 
situated at the extremity of the circuit of smoke, aud 
close to the point where the feed- water arrived, and he 
remarked that the water vapor contained in the smoke 
was liable to condense there, and the effect of this con- 
densation might be added to that of the infiltration, and 
favor the oxidation of the sulphurous acid into sul- 
phuric acid; the water from the boiler concentrating 
itself chiefly along the edge of the cover-plate over the 
joint of the two plates, which prevented it descending, 
It would thus moisten the deposits in this part, which 
the form of the brick work prevented being regularly 
cleaned, and thus favored oxidation of the sulphurous 
acid in sulphuric acid on the surface of the metal. M. 
Douville found large scales of oxide of iron on the cor- 
roded parts, and also sulphur in some form of combina- 
tion. 

"2. The accident at the Ougree works presented 
more conclusive evidence; in this case, sulphuric acid 
was actually found in a free state, as well as in the form 
of sulphate of iron. The following are the circum- 
stances of this case: The boiler was horizontal and 
cylindrical, with two water tubes below, and it was 
heated by the flames of the puddling furnaces. These 
flames at once enveloped one of the tubes and half the 
lower part of the boiler itself, and, making the circuit, 
heated the other half and second tube. The tube to the 
right of which the flames debouched was torn open in 
much the same manner as the superheater in the former 



SULPHUR A CAUSE OF CORROSION IN BOILERS. 165 

case; the fracture, taking two courses perpendicu- 
larly, one in the iron plate itself, the other along a riv- 
eted seam. The thickness of the iron was reduced to 
about one millimeter (one twenty-fifth of an inch), at 
the edges of the first rent. The corrosion was all 
exterior. 

"Two samples of the soot, etc., left by the smoke in 
the parts destroyed were analyzed ; they gave sulphate 
of iron between fifty-two and fifty-three per cent., and 
free sulphuric acid in one sample 1.42, and the other 
nearly twelve per cent. Soot from other parts also con- 
tained sulphuric acid, but not enough to have any 
sensible result on the iron. 

"The action is thus explained: the soot, etc., is 
deposited during the working of the puddling furnaces 
in an entirely dry state, but when the fires are put out, 
the air, loaded with humidity, enters and converts the 
soot into a paste; the oxidation of the sulphurous acid 
then occurs, and the iron is in the best condition to be 
attacked. The corrosive action is thus going on all the 
time the boiler is not in work, in parts that could not 
be cleaned out, while no such action occurred where the 
soot had been cleared away. 

" 3. Examples of exterior corrosion by condensation 
of steam suspended in the smoke on the colder portions 
of boilers were pointed out by M. Meunier Dollfus some 
years since, and published; one of these cases was 
observed at the works of M. Charles Kestner, at Thaun. 

"The works contained two cylindrical boilers with 
three tubes, and between them, in the same brick-work, 



166 COMBUSTION OP COAL. 

six re-heaters arranged in pairs on three stages. The 
flames circulated under the three tubes, twice around the 
boiler itself, and then in the three stages of the re-heater 
from above downwards. The feed-water traversed in 
the opposite direction. Generally only one of these 
boilers was used at a time, working night and day, but 
less actively at night. 

"In an experiment, when the feed-water arrives at a 
temperature of 68° Fahr., the water of the first re-heater 
below only marked 86° Fahr. on issuing, and that of the 
third re-heater at 122° Fahr. On the other hand, the 
temperature of the smoke and gases at the issue of the 
third re-heater did not exceed 302° Fahr. in the day 
and 212° Fahr. at night. At the end of two years' 
working, under the above conditions, the re-heaters 
w T ere already attacked, and at the end of six years, 
although the iron was of excellent quality, they were so 
reduced that they had to be replaced. The corrosion 
took place on the colder portions of the re-heaters, and 
it was found that the first cause was the sulphurous 
acids contained in the condensed steam deposited by 
the smoke, and in the presence of air and of these acid 
waters, oxidation of the iron readily occurred, with the 
subsequent production of sulphate of iron. 

"4. Observations have also been made on this cause 
of destruction of boilers, by M. Cornut, Engineer of the 
Association of the Proprietors of Steam Apparatus of 
the North of France, at Lille. He often observed 
exterior corrosions, which he attributed to the action of 
smoke, and which he found absolutely confined to those 



SULPHUR A CAUSE OF CORROSION IN BOILERS. 167 

parts of the iron which were wetted by infiltration or 
accident. 

" 5. Resuming the facts stated above, the transform- 
ation of sulphurous into sulphuric acid, under the action 
of water, or steam and air, in presence of a metal is not 
new. This property of sulphurous acid has even been 
employed practically in treating certain minerals, and 
in purifying the neighborhood of certain metallurgical 
establishments. We may mention as a notable instance, 
the process of M. Lamine, for the manufacture of sul- 
phate of alumina at Ampain, in Belgium, and the treat- 
ment of certain oxides of copper on the banks of the 
Rhine. Such applications as these, not of recent date, 
should have awakened engineers to the possibility of 
the destruction of the iron boilers by a like action, but 
such was not the case, and it remains to be noted that if 
the fact is now well known, the subject requires to be 
most carefully studied in all its details, some of which 
can not fail to be of practical importance." 

Conclusion — The whole may be summed up as fol- 
lows : In the matters deposited on the plates of boilers, 
at a certain distance from the fire, and which are ren- 
dered humid by any accidental cause, the sulphurous 
acid carried forward by the combustion gases, attack 
the iron by the formation of sulphate of iron. 

The attack may occur while the boiler is heated 
through an escape of water, from the boiler itself, by 
infiltration through the brick work, or by the condensa- 
tion of steam in the flames and smoke in contact with 



168 COMBUSTION OF COAL. 

iron plate relatively cold. It may also occur when the 
boiler is not in use, by means of the penetration of the 
air into the flues. 

The diverse origin of the corrosive action points out 
the nature of the precautions to be taken to obviate 
the destruction, except as applies to the condensation of 
the vapors, on which subject many arrangements have 
been recommended, but have not yet obtained the sanc- 
tion of experience. 

The precautions, alluded to above, are only such as 
should be taken in ordinary practice for the preserva- 
tion of apparatus; that is to say, careful design and 
construction, and systematic and complete cleansing. 

ASHES AND CLINK ER 

Every variety of mineral fuel contains more or less 
incombustible matter called ashes. The presence of 
this incombustible substance in coal is due in part to 
the inorganic matter contained in the plants of which 
the coal is formed, and partly by the earthy matter in 
the drift of the coal period. The percentage of ash 
varies considerably for different coals, but it is generally 
less in the anthracite than in the bituminous varieties. 

Upon analysis coal ashes are found to consist princi- 
pally of silica, alumina, lime, and oxide and bisulphide 
of iron. The nature and color of ashes are greatly 
modified by the proportions in which the above sub- 
stances are united in the composition. In the following 
analysis, as in all analyses of coal ashes, silica and 
alumina predominate. 



ASHES AND CLINKER. 169 



Analysis of ashes of Pennsylvania anthracite coal, 
by Professor W. ~R. Johnson : 

Silica 53.60 

Alumina 3G.69 

Sesquioxide of iron 5.59 

Lime 2.86 

Magn esia 1.08 

Oxide of Manganese .19 

100.01 

The next analysis is from the geological survey of 
Ohio : 

Bituminous coal. Percentage of ash, 5.15. 

Silica 58.75 

Alumina 35.30 

Sesquioxide of iron 2.09 

Lime 1.20 

Magnesia 0.68 

Potash and soda 1.08 

Phosphoric acid 0.13 

Sulphuric acid 0.24 

Sulphur, combined 0.41 

99.88 

An ordinary sample of block coal, from Clay county, 
Indiana, was analyzed by Professor E. T. Cox, and 
found to contain, 

Fixed carbon 56.50 

Gas 32.50 

Water 8.50 

Ash 2.50 

100.00 



170 COMBUSTION OF COAL. 

Specific gravity, 1.285 

Coke : Not swollen, laminated, lusterless. 

Composition of Ash : Color, white. 

Iron, sesquioxide 82 

Alumina 1.20 

Silica, lime, magnesia, etc 48 

2.50 

Of the sulphur present in the coal, 

.947 was in combination with iron. 
.483 with other constituents. 



1.430 per cent, of sulphur in the sample. 

Nearly every variety of coal contains more or less 
iron-pyrites ; this is the probable source of the oxide of 
iron in the ashes; the greater part of the sulphur being 
expelled by heat, its equivalent of oxygen unites with 
the iron, and with which hydrogen also combines, form- 
ing the sesquioxide of iron of the analysis. The 
amount of oxide of iron, present in ashes, is one of 
great importance, especially as it unites with the potash, 
soda, lime and silica, also present, to form clinker. The 
presence of iron in ashes, when in any considerable 
quantity, may be detected, without analysis, by the red 
color imparted to them. When the amount of iron is very 
small, or not sufficient to tinge the ashes, they are then 
usually white; so the terms red-ash and ivhite-ash may 
be a sort of index by which we may judge of the prob- 
able nature of the ashes, whether they will clinker in 
the fire or not. The intensity of the red color, taken 
in connection with the amount of ashes in coal, may 



ASHES AND CLINKEK. * 171 

also serve as an indication of the proportion of sulphur 
existing in the state of pyrites. 

The particular objection to the combination and fusing 
of the silica, lime, potash, soda, etc., in the ashes of the 
coal into a vitreous mass is, that unless the greatest care 
is exercised, it will accumulate upon the grate-bars in 
sufficient quantity as to exclude the passage of the air 
needed for combustion, and thus lower the temperature 
of the furnace. 

These several constituents are variable in their nature, 
and by the forms they take under different intensities of 
combustion, much affect the efficiency of the coals to 
which they belong (23). Being differently fusible them- 
selves, and affecting differently the fusion of each other, 
no two of the earths, alkalies, or metallic oxides of the 
ashes, but differ in their agency when subjected to an 
elevated heat, and their mutual reactions are moreover 
changed, as the temperatures are changed to which they 
are exposed. It hence arises that the residue from many 
coals melts to a large extent, under no very intense com- 
bustion, into various descriptions of hard semi- vitreous 
slags; others yield a less stony clinker; and some again, 
at a far more elevated heat, result only in a partially 
agglutinated, spongy, open cinder, or even in a pulveru- 
lent or flaky ash. There are, perhaps, no coals whose 
ashes, when exposed to the extremest heats procurable 
by artificial blasts, will not soften to a cohering cinder, 
or even melt in part into a stony clinker; but as the 
tendencies to these several degrees of fusion are very 
various, it proves to be a distinction affecting the prac- 



172 COMBUSTION OF COAL. 

tical value of coals, which is of the utmost importance. 
In domestic consumption, where the heat of combustion 
is comparatively moderate, the quantity rather than the 
quality or fusibility of the ashes is the point of greatest 
consideration ; but where an excessive and melting heat 
is required, as in many modes of generating steam, the 
practicability of employing a coal at all will oftentimes 
be determined by this one quality of clinkering of the 
ashes. In all such circumstances, those coals are best 
the ashes of which are of a nearly pure white, and 
which, with large amounts of silica and alumina in their 
composition, contain little or no alkali, nor any lime, 
nor oxide of iron. Of this character, are the earthy 
residue of the best white-ash anthracites, of Pennsyl- 
vania, and, in an eminent degree, the ashes of some of 
the semi-anthracites. 

In general, it requires a high temperature to fuse 
these ingredients when taken by themselves, but the 
presence of the oxide of iron tends to lower the point 
of fusion, and thus increases the difficulty. 

The grate bars recommended for any coal, the ashes 
of which are liable to clinker, are any of those forms 
which may, while in position and in use, be either 
shaken, tilted, or revolved without injuriously breaking 
up the fire. 

APPARATUS FOR GAS ANALYSIS (19). 

As a rule, gaseous agents hold a very important 
position in technical chemistry, whether atmospheric air 
be employed in ordinary cases, or under circumstances 



APPARATUS FOR GAS ANALYSIS. 173 

in which the employment of other gases is desirable for 
chemical analysis. In most of the latter cases special 
apparatus is desirable for the production of such gases. 
If we take metallurgical analysis, for example, as a 
branch of technical chemistry, we shall frequently find 
that remarkable and crucial differences occur according 
to the gas employed. The question of their quantity 
frequently becomes of importance in regard to first indi- 
cations for qualitative and quantitative analysis, as an 
instance of which may be mentioned the free combus- 
tion of any form of carbon, supposing the amount of 
air present to have been entirely utilized, taking at the 
same time the relation of the weight of air to that of 
consumed carbon. But in all such cases great uncer- 
tainty exists in the exact estimation of such relations. 

Despite the advantage of its study, that of gaseous 
analysis has scarcely yet found its proper position in 
technical chemistry, although the latter branch of sci- 
ence has of late made very rapid strides. The reason of 
this may be partly explained on the ground that there 
is much difficulty in manipulating with all gases, result- 
ing from the delicacy of the apparatus employed in the 
laboratory, and the usual slowness of such operations. 

Although comparatively few gases are met with in 
technological operations, yet their action predominates 
over almost any other agent, and consequently it is 
desirable to arrange such an apparatus more simple than 
those usually employed in laboratories, without the use 
of the pneumatic trough of water or mercury (both 
frequently inconvenient), nor requiring barometrical or 



174 



COMBUSTION OF COAL. 



thermometric corrections hitherto considered indispen- 
sable. It is desirable, in fact, to present such an 
arrangement as shall be readily available for the use of 
ordinary intelligent workmen, so as to furnish not only 
ready but comparatively trustworthy indications. 

For the purpose just referred to, M. De H. Orsat, of 
Paris, has suggested the apparatus here illustrated. 




Figure 4. 

"The apparatus consists essentially as a graduated 
pipe, A B, placed in a receiver filled with water, 
intended to preserve a constant temperature, a most 
important point in gas analysis. This graduated tube 
communicates at A with a horizontal capillary tube, fur- 
nished with a stop-cock, (7, through which the gas 
passes into the measuring apparatus. The lower por- 
tion of the measuring arrangement is connected by an 
India rubber tube, 0, to a gas jar, D, by means of an 
opening at the bottom; this jar being partly filled with 
water, the water in this jar may be lowered by sucking 



APPARATUS FOR GAS ANALYSIS. 175 

out, or raised by blowing into it. The horizontal tube 
is connected by two branches furnished with two stop- 
cocks, G and H, with two bell-glasses placed in the 
eprouvettes, E and F, which contain the liquids 
intended to absorb the gases under examination or use. 
The first eprouvette, E, contains a solution of caustic 
potass. The bell-glass is entirely filled with small tubes 
of glass, open at both ends, and intended by capillary 
and other action to facilitate, as far as possible, the rapid 
absorption of the gas in the bell-glasses. 

" The second eprouvette, F, contains an ammoniacal 
solution of chloride of ammonium (sal-ammoniac). The 
interior of the second bell-glass is filled with metal foil, 
consisting of copper, in repeated coils, so that at the 
same time oxygen shall be absorbed, oxide of carbon, 
in the presence of the saline solution, by chemical action, 
combining with the physical action of the tubes in the 
first eprouvette. 

"For the sake of safety, a fourth stop-cock allows 
the escape of gas, which would otherwise remain in the 
apparatus. If the tube JV, which brings the gas, has 
great length, it is easily cleaned by the arrangement, 
marked K L M,hj water. It is sufficient to send a few 
decimeters* of water by the tube, K M, to produce an 
up-clraft in L, to act as a balance to the gas in N. A 
litre of water, or say, a quart, English, is sufficient to 
effect this in a tube of four millemeters (0.15 in.) in 
diameter. By connections with the tube iV, by India 
rubber piping, any apparatus employed in gas analysis 

:: A decimeter = 3.94 inches. 



176 COMBUSTION OF COAL. 

may be employed, and by very simple arrangements the 
outer apparatus may be applied for any of the objects 
hereafter named. 

" The explanation of the use of the apparatus will 
be better understood by the following remarks : 

"The first bell-glass receives gases absorbable by 
means of a solution of caustic potass; the second receives 
those which, being not absorbed by the first, are absorb- 
able by means of a solution of copper. For example, in 
the ordinary combustion analysis, the first absorbs car- 
bonic acid, and the second oxygen and carbonic oxide. 

" In the ordinary state of combustion, both of these 
gases are given off, and some inconvenience might be 
supposed to arise from the fact, but the difficulty is 
more apparent than real. 

"They are easily separated on account of their 
chemical individuality. 

"In certain cases, it happens that carbonic oxide 
may remain with oxygen, but even in this case 
an approximative result of their proportions may be 
obtained, when the combustible matter does not afford 
free oxygen nor hydrocarbons. Practically, the oxygen 
afforded by the atmosphere does not change its volume 
by aiding to produce carbonic acid, while its volume is 
doubled by producing carbonic oxide. It, therefore, 
becomes a simple question of calculation to determine 
the nitrogen in the measured tube, and any other deter- 
mination depending on measurement in the absence of 
absorption. 

"In certain cases the addition of a third bell-glass 
would be desirable, especially in the event of the respect- 



APPARATUS FOR GAS ANALYSIS. 177 

ive presence of oxygen and carbonic oxide requiring to 
be determined. The third glass should then be sup- 
plied with pyrogallate of potash, or stick of phospho- 
rus. Sulphurous acid may also be determined by the 
apparatus, also hydrosulphuric acid (sulphureted hydro- 
gen), and chlorine. In special cases the apparatus might 
be employed for estimating gases which present them- 
selves in a separate form; sulphurous acid, for example- 
in the presence of carbonic acid, may be estimated by a 
solution of potass in sulphuric acid (and water), or by 
the permanganate of potash. When gases very solu- 
ble in water are to be examined, as, for example, sul- 
phurous acid, there should be a substitute of glycerine 
in the bottle or flask, D, in place of water." 

The value of this apparatus largely rests on the fact 
that it may be placed in the hands of an ordinary work- 
man for qualitative analysis to control his operations. 
At the same time its indication may be controlled by 
very simple arrangements, so that the manager may 
notice the indications afforded by each apparatus, with- 
out the knowledge of those, using it. It is applicable 
to a large variety of purposes, as, for example, the esti- 
mation of the gaseous products of reverbatory furnaces, 
puddling furnaces, the Bessemer, and Danks arrange- 
ments for dealing with pig-iron, the production of car- 
bonic acid in lime-burning, sugar works; the manufac- 
ture of alkaline carbonates, wine, beer, and vinegar 
production, with an immense variety of technical and 
other purposes. 
(13) 



CHAPTEE IX. 

THERMAL POWER OF FUELS. 

Heat Developed by Chemical Action — Favre and Silberman's 
Apparatus — Units of Heat Evolved by Elemental Combus- 
tion — Heat Developed by the Combustion of Coal — Allotropic 
States of Carbon — Proximate Constitution of Coal — Experi- 
ments of Scheurer-Kestner and Meunier-Dollfus on the 
Calorific Power of Coal — Thompson's Calorimeter — Manner of 
Conducting Experiments — Evaporative Power of Coal — Object 
in Reducing Evaporation to, from and at 212° Fahr. 

The total heat of any combustible may be calculated, 
if its proximate or elementary analysis is known, by 
means of data analogous to that furnished by Favre and 
Silberman, or it may be determined by means of a 
calorimeter, similar to that of Thompson, described in 
this chapter. 

HEAT DEVELOPED BY CHEMICAL ACTION. 

The apparatus used by Favre and Silberman for 
measuring the heat evolved by the combustion of vari- 
ous substances in oxygen gas is represented, with the 
omission of minor details (13), in figure 5. C is a ves- 
sel of gilt brass plate, immersed in a water-calorimeter, 
A A, of silvered copper plate, and the latter is enclosed 
in an outer vessel, B B, the space between A and B 
being filled with swan-down, to prevent the escape of 
heat from the water in A. The vessels A and B are 
closed with lids having apertures for the insertion of 
tubes and thermometers. The combustions are per- 



HEAT DEVELOPED BY CHEMICAL ACTION. 



179 



formed in the vessel C, into which oxygen is introduced 
through the tube, c d, and the gaseous products of the 
combustion escape by the tube, e f g A, the lower part of 
which is bent into numerous coils, to facilitate, as much 
as possible, the transmission of the heat of these gases 
to the water in the calorime- 
ter. The extremity, h, of this 
tube is connected with a gaso- 
meter, or with an absorbing 
apparatus. To insure uniform- 
ity of temperature in the wa- 
ter, a flat ring of metal, i i, is 
moved up and down by means 
of the rod, K i. Combustible 
gases were introduced into the 
vessel 0, by means of fine tubes, 
the gas being previously set on 
fire at the • aperture. Solid 




Figure 5. 

bodies were attached to fine platinum wires suspended 
from the lid of the calorimeter ; the liquids were burned 
in small capsules, or in lamps with asbestos wicks; 
charcoal was disposed in a layer on a sieve-formed bot- 
tom, through the openings of which the oxygen had 
access to it. The heat evolved was measured by the rise 
of temperature of the known quantity of water in the 
calorimeter. 



180 



COMBUSTION OF COAL. 



Table XIX. 

Showing the Total Quantities of Heat Evolved by the complete 
Combustion of one pound of Combustible with Oxygen; adapted 
from the kesults obtained by favre and sllberman. the unit 
of weight in this table being one pound, and the unit of tem- 
perature one degree fahr. (from 39° to 40°). 



SUBSTANCE. 



PRODUCT. 



UNITS OF HEAT 



GASES. 

Hydrogen 

Carbonic oxide 

Marsh gas 

Olefiant gas „ „ — 

LIQUIDS. 

Oil of turpentine.... ... 

Alcohol 

Spermaceti (solid) 

Sulphate of carbon 

SOLIDS. 

Carbon (wood charcoal) 

Gas coke 

Graphite from blast furnaces 

Native Graphite 

Sulphur (native) 



H 

CO 
CH 4 
C2 H4 

CioH]6 

C 2 H s O 

C32HG4O2 

cs 2 



Phosphorus (observed by An- 
drews) , 



H 2 
C0 2 
CO2&H2O 
C0 2 &H 2 

C0 2 &H 2 
C0 2 &H 2 
C0 2 &IL,0 

C0 2 & S0 2 

CO 
C0 2 



so 2 . 
P205 



62,032 

4,325 

23,513 

21,343 

19,533 

12,931 

18,616 

6,122 

4,451 
14,544 

14,485 

13,972 

14,035 

4,048 

10,715 



HEAT DEVELOPED BY THE COMBUSTION OF COAL. 

This may be determined theoretically by taking the 
units of heat evolved by each element in the coal separ- 



HEAT DEVELOPED BY THE COMBUSTION OF COAL. 181 

ately — allowing certain deductions — and adding them 
together. This requires then, an elementary analysis to 
begin with. Assuming, for example, that a certain 
sample of coal, weighing one pound, is analyzed, and is 
found to contain, 

Carbon 81 

Hydrogen 05 

Oxygen 04 

Nitrogen, ash, etc 10 

1.00 

and that the sulphur and other impurities in the coal 
he disregarded, we proceed to estimate its calorific 
power in this way : 

UNITS. PER CENT. 

Carbon 14,500 X .81 = 11,745 

units of heat in the carbon. 

Since oxygen and hydrogen unite to form water, the 
whole of the oxygen must be deducted, together with its 
equivalent of hydrogen, before we can determine the 
calorific power of the latter, for the available hydrogen 
in the coal is only that above the quantity required to 
unite with oxygen, as stated above. 

Oxygen unites with -L. of its own weight of hydrogen 
to form water; and, 

pound of hydrogen neutralized by the presence of 
oxygen in the coal, leaving 

.05 — .005 = .045 



182 COMBUSTION OF COAL. 

pound of available hydrogen ; then, proceeding as "before : 

UNITS. PER CENT. 

Hydrogen 62,032 X .045= 2,791. units. 

adding the 

Carbon 14,500 X .81 =11,745. units. 

Total....' 14,536. 

units of beat in one pound of coal of the composition 
assumed. 

This is called the theoretical calorific power of coal. 

The nitrogen and ash being inert, are simply dilut- 
ants, and no account is taken of them. 

This appears, at first sight, a very simple and easy 
method of determining the calorific power of coal, but 
it is open to serious objections ; one is, the elementary 
analysis demanded as a starting point; another, is the 
uncertain value of carbon. 

The following table is compiled from the researches 
of Favre and Silberman 

Table XX. 



VARIETIES OF CARBON. 



Diamond 

Graphite — artificial 

Graphite — native , 

Carbon from gas-retorts 
Charcoal from wood , 



UNITS OF 
HEAT. 



13,986 
13,972 
14,035 
14,485 
14,544 



HEAT DEVELOPED BY THE COMBUSTION OF COAL. 183 

These substances, it may be remarked, are practically 
elemental, yet, the difference between the two extremes 
are five hundred and fifty-eight heat units. 

How much of this difference is due to the allotropic 
condition of the carbon is not easily stated; it is possible, 
and altogether probable that it has much to do with it. 

It might be said that as diamonds, graphite, and gas 
carbon are not employed as fuel, it is of little conse- 
quence what difference there may be between them. 
This would appear to the superficial observer as a 
•'practical" truth, but it is not so. It must be remem- 
bered these are not compounds of carbon, but pure car- 
bon. If the theoretical power of carbon is an uncertain 
quantity, then, a guess is as good as a calculation. 

The various kinds of coal found in this country, 
passing through an innumerable series of gradations, 
from the least cohesive of the bituminous varieties, to 
the hard crystalline Lehigh anthracite, adds emphasis to 
the question instead of waiving it. 

Assuming the calorific power of coke to be known, 
it is desirable to know whether the volatile portion of 
the coal yields the calorific power ascribed to it by 
calculating the elements separately, and adding them 
together; also, whether the sum of the heat units of 
the coke and volatile matter is more or less than the 
units of heat given off by the coal during the actual 
burning. Various calorimeters have been devised to 
ascertain, if possible, a close approximation to the 
actual calorific power of any given sample of coal with- 
out undergoing any analysis whatever. 



184 COMBUSTION OF COAL. 

This seems all the more desirable as the proximate 
constitution of coal is wholly unknown (20); we are 
ignorant whether force is liberated or absorbed during 
the decomposition — previously to, or at, the moment of 
combustion — of the various compounds of carbon, 
hydrogen and oxygen, of which the organic part of coal 
must be composed. Again, the hydrogen and oxygen 
are present in the solid state, and we are unable to 
determine what amount of force may be absorbed dur- 
ing their conversion into the gaseous state. 

EXPERIMENTS OX THE CALORIFIC POWER OF COAL. 

M. M. Scheurer-Kestner and Charles Meunier-Doll- 
fus, have, within a few years past, made a special study 
of different coals with reference to their caloritie power, 
making use of a modified form of the Favre and Silber- 
man calorimeter, described on page 179 in this volume : 
the modifications were such that the carbonic acid pro- 
duced on combustion was cooled with great rapidity, 
whereby the quantity of carbonic oxide formed was 
much reduced. It has not been found possible to pre- 
vent the formation of some carbonic oxide during the 
combustion of carbon, even under the most favorable 
conditions, but the amount produced in each experiment 
can be accurately determined by passing the products of 
combustion first through a solution of potash, which 
absorbs the carbonic acid, and afterward through a tube 
containing black oxide of copper heated to redness. 
l>y this means carbonic oxide can be converted into car- 



HEAT DEVELOPED BY THE COMBUSTION OF COAL. 185 

bonic acid, which may be collected in a solution of pot- 
ash and weighed. 

For the sake of comparing the experimental with 
the theoretical values of the coals as deduced from their 
composition in the manner before described, they 
reduced their experimental results, and calculated them 
as though the coals had consisted wholly of the organic 
constituents, excluding the ash and the hygroscopic 
water. They made corrections for the carbon, which, in 
their experiments in the calorimeter, was retained in the 
ash, and also for the hydrogen and carbonic oxide which 
escaped combustion ; but they appear to have taken no 
account of the sulphur in the state of sulphide, which 
all coal contains, and which would, in greater or less 
degree, according to its quantity, add to the amount of 
heat produced in the calorimeter. 



186 



COMBUSTION OF COAL. 





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HEAT DEVELOPED BY THE COMBUSTION OF COAL. 



187 



From an inspection of the table, it will be seen, that 
in every case the experimental calorific power of the 
coal considerably exceeds the calculated result, and that 
coals with nearly the same percentage composition, so 
far as regards organic constituents, may differ widely in 
calorific power. 

Table XXII. 

Showing the Experimental Calorific Power of Different Coals 
and Lignites as observed by Scheurer-Kestner and Metjnier- 
Dollfus. 



COMBUSTIBLE. 



COAL. 

Ronehamp, three samples 

Saarbruck, seven samples 

Creusot, four samples 

Blanzy — Montceau 

Blanzy — Anthracitic 

Angin 

Denain 

English— Bwlf 

English— Powell-Duffryn 

Russian — Grouchefsdi Anthracite 
Russian — Miouchi, Bituminous.... 
Russian — Goloubofski, naming .. . 

LIGNITES. 

Rocherblea 

Bohemia, Bituminous 

Russian, Toula 

Lignite, passing to fossil "wood 

Fossil wood, passing to lignite 



GASEOUS ELEMENTS. 



PER 
CENT. 

88.59 
81.10 
90.60 
78.58 
87.02 
84.45 
83.94 
91.08 
92.49 
96.66 
91.45 
82.67 

72.98 
76.58 
73.72 
66.51 
67.60 



PER 
CENT. 

4.69 
4.75 
4.10 
5.23 
4.72 
4.21 
4.43 
3.83 
4.04 
1.35 
4.50 
5.07 

4.04 
8.27 
6.09 
4.72 
4.55 



H ~ * 

5 o o 
o 5s 



PER 
CENT. 

6.72 

14.15 

5.30 

16.19 

8.26 

11.32 

11.63 

5.09 

3.47 

1.99 

4.05 

12.26 

22.98 
15.15 

20.19 
28.77 
27.85 



a 



fe " Q « 



fc w 






UNITS. 
16,416 
15,320 
16,994 
14,985 
16,400 
16,663 
16,290 
15,804 
16,108 
14,866 
15,651 
14,438 

11,670 
14,263 
13,837 
11,444 
11,360 



188 



COMBUSTION OF COAL. 



The fuel is assumed to be dry and pure — without 
any ash. 

THOMPSON'S CALORIMETER. 

The object of this instrument is to give approxi- 
mately, by means of a simple experiment, the theoretical 
evaporative power of any fuel submitted to investiga- 
tion (20). 

" It consists of a glass cylinder, A, 
closed at the lower end only, to con- 
tain a given weight of water. 

"B is a cylindrical copper vessel, 
called the condenser, closed at one end 
with a copper cover, in which is fixed 
a metal tube C, communicating with 
the interior of the vessel B, and fitted 
at its upper extremity with a stop- 
cock. The other end of B is open, 
and it is perforated near the open end 
by a series of holes, bb. 

"D is a metal base upon which B 
is fixed by means of three springs, 
which are attached to _D, and press 
against the internal surface of B, but 
which are omitted from the wood cut 
for the sake of clearness. A series of 
holes is arranged round the circum- 
ference of D to facilitate raising the 
apparatus through the water. 

"E is a copper cylinder, called the furnace, closed at 
the lower end only, which fits into a metal ring or seat 
on the center of D. 




Figure 6. 
Scale one-fourth full size. 



Thompson's calorimeter. 189 

" The manner in which results are obtained is as 
follows : A known weight of the fuel is burnt by means 
of chlorate of potash and nitre at the bottom of a vessel 
containing a known weight of water ; the heat pro- 
duced by the combustion of the fuel is communicated 
to the water, and from the rise in temperature of the 
latter is calculated the number of parts of water which 
the combustion of one part of the fuel will raise one 
degree in temperature: this number being divided by 
the latent heat of steam (537 or 967 units, according 
as the centigrade or Fahrenheit scale is employed), 
gives the evaporative power of the fuel, i. e., the num- 
ber of pounds of water (supposed to pre-exist at the 
boiling point) which one pound of the fuel is theoreti- 
cally capable of evaporating. 

" In the instrument, as constructed by the manufac- 
turer, it is intended that thirty grains of the fuel should 
be burnt, and that 29,010 grains (or nine hundred and 
thirty-seven times this weight) of water should be 
employed; hence the rise in the temperature of the 
water, expressed in degress Fahrenheit, is equal to the 
number of pounds of water w^hich one pound of the 
fuel theoretically will evaporate; but ten per cent, is 
directed to be added to this number, as a correction for 
the quantity of heat absorbed by the apparatus itself, 
and consequently not expended in raising the tempera- 
ture of the water. 

" In addition, the gaseous products of combustion 
generally escape from the surface of the water whilst 
sensibly warm. Whether this loss of heat is covered by 



190 COMBUSTION OF COAL. 

the above correction, I am unable to state; that it is 
not unimportant, has been proved, in my laboratory, by 
enclosing the lower part of the condenser within a large 
metallic cylinder, perforated all over with small holes, 
so that the escape of gases from the water was retarded 
when the experimental results obtained were notably 
higher. Thus, in comparative experiments upon a 
Welsh steam coal, it was found that its theoretical 
evaporative power was raised from 14.41 to 14.96 pounds 
of water, by enclosing the condenser in the manner 
described. The colder the water, the smaller will be 
this loss of heat, owing to the gases being more 
thoroughly cooled. 

"The experiment is conducted in the following man- 
ner: Thirty grains of finely-powdered fuel is intimately 
mixed with from ten to twelve times its weight of a 
perfectly dry mixture of three parts of chlorate of 
potash and one part of nitre; the resulting mixture, 
which, for the sake of distinction, may be called the 
fuel-mixture, is introduced into the furnace, E y and care- 
fully pressed or shaken down. The end of a slow fuse, 
about half an inch long, is next inserted in a small hole 
made in the top of the fuel-mixture, and is fixed there 
by pressing the latter around it; the furnace is then 
placed in its seat on the metal base, _D, the fuse lighted, 
and the condenser, B, with its stop-cock shut, fixed 
over the furnace. 

" The cylinder, A, is previously charged with 29,010 
grains of water, the temperature of which must be 
recorded, and the apparatus is now quickly submerged 



EVAPORATIVE POWER OF COAL. 191 

in it. The fuse ignites the fuel-mixture, and when the 
combustion is finished (indicated by the cessation of the 
bubbles of gas, produced by the combustion, which rise 
through the water), the stop-cock is opened, and the 
water enters the condenser by the holes, bb. 

"By moving the condenser up and down, the w r ater 
is thoroughly mixed and acquires a uniform temperature, 
which is then recorded. By adding ten per cent, to the 
number of degrees Fahr. which the water has risen in 
temperature, the theoretical evaporative pow T er of the 
coal is at once approximately determined. 

" The furnace shown in figure 6 is intended to be 
used when bituminous coals are to be operated upon ; 
but in experimenting on coke, anthracite and other 
difficult combustible fuels, a wider and shorter furnace 
is preferred, and the fuel mixture should not be pressed 
down." 

Evaporative Power of Coal — By this is meant the 
number of pounds of water, which, under certain condi- 
tions, are capable of being evaporated per pound of 
coal. It is essential to the obtaining of accurate results, 
that the temperature of the feed water and the tempera- 
ture of evaporation should both be ascertained, and the 
total heat per pound of water computed. That total 
heat being divided by 966, the latent heat of evapora- 
tion of a pound of water at 212°, gives a multiplier, by 
which the weight of water actually evaporated by each 
pound of fuel is to be multiplied, to reduce it to the 
equivalent evaporation from and at 212°; that is, the weight 



192 COMBUSTION OF COAL. 

of water which would have been evaporated by each pound of 
fuel, had the water been both supplied and evaporated at 
the boiling point corresponding to the mean atmospheric 
pressure. 

The weight of water so calculated is called the 
evaporative power of the fuel. 

The object of reducing evaporative results in prac- 
tice to equivalent evaporation from and at 212°, is to 
afford an intelligible basis of comparison between differ- 
ent kinds of fuel. 

To make such a comparison it is necessary to know 
the pressure and temperature of the steam; the temper- 
ature of the feed water; the number of pounds of coal 
burned on the grate (deducting the ashes, if the net 
combustible is desired) ; and the number of pounds of 
water evaporated in a given time. From these last two 
items the ratio of coal, or net combustible, to evapora- 
tion can easily be determined by dividing the pounds of 
water evaporated, by the pounds of coal burned in an 
hour, a day, or any other given time. 

Example — A boiler evaporating eight pounds of 
water per pound of coal (net), the temperature of the 
feed water being 85° Fahr., and the pressure of steam in 
the boiler seventy-live pounds per square inch, above the 
atmosphere ; what is the equivalent evaporation per 
pound of coal (net) at atmospheric pressure from and 
at 212°? 

The total heat required to generate one pound of 
steam from water at 32° Fahr., under a constant pressure 



EVAPORATIVE POWER OF COAL. • 193. 

of seventy-five pounds per square inch is 1176 units of 
heat. The water entering the boiler at a temperature* 
of 85° instead of 82°, there is a gain of 85 — 32 = 58. 
degrees. Then, 

] 176 — 53 = 1123 units of heat. 

The units of heat required to convert one pound of 
w T ater at 212° into steam, at atmospheric pressure,, is* 
966. Then, 

1123-^-966 = 1.16, the multiplier. 

1.16 

8 pounds of coal. 

9.28 = 

the equivalent evaporation per pound of coal (net), at 
atmospheric pressure, from and at a temperature of 212°. 

Second Method — When the total heat of combustion 
of one pound of combustible is known. 

In this case, the equivalent evaporative power of the 
combustible at atmospheric pressure, from and at a tem- 
perature of 212°, may be determined by dividing the 
number of heat units of the combustible by 966, the 
number of heat units required to convert water at 
212° into steam at atmospheric pressure. 

Example 1 — What number of pounds of w r ater ? 
at 212°, will one pound of bituminous coal, having 
13,624 heat units as its total heat of combustion, convert 
into steam at atmospheric pressure? 



966 

(14) 



14.1 pounds of water 



194 COMBUSTION OF COAL. 

Example 2 — The same as the preceding except the 
feed water to be at 64° instead of 212° ? Then, 

212° — 64° = 148° difference. 
966° + 148° = 1114° the new divisor. 
1 , ni =12.23 pounds of water. 

And in this manner for any temperature between 32° 
and 212°. 







CHAPTER X. 



HEAT. 



Theory of Heat — Mechanical Force — Chemical Action — Relation of 
Atomic Weights to Specific Heat — Specific Heat of Simple 
Gases — Specific Heat and Atomic Weight of Elementary Sub- 
stances — Specific Heat — Specific Heat of Water in its Three 
States — Specific Heat of Fuels — Specific Pleat of Gases — Latent 
Heat — Latent Heat of Fusion — Lat-ent Heat of Evaporation — 
Mechanical Theory of Heat — Joule's Equivalent — Apparatus 
Employed by Joule — Unit of Heat. 

The theory of heat now accepted is known as the 
dynamical, or the mechanical theory, and is so called 
because it is believed that heat and mechanical force are 
identical, and convertible one into the other. 

The relation between heat and mechanical force is 
now expressed by a numerical equivalent, which is so 
nearly true that it serves to show not only the probable 
permanence of this theory, but indicates, also, that these 
relations are determined by a fixed numerical law. 

From the vast number of experiments in the genera- 
tion of heat by mechanical processes; by friction; by the 
arrest of motion, either gradually or by percussion ; by 
the change in quantity of heat observed in the case of 
expansion, etc., has led investigators to the conclusion 
that heat is simply a motion of ultimate particles, and 
that the molecular structure of bodies has much to do 
with their capacities for heat; and, an increase or 
decrease of temperature is simply an increase or decrease 
of molecular motion. 



196 COMBUSTION OF COAL. 

As all chemical changes are either atomic or molec- 
ular, and as all differences in the temperature of bodies 
are due to the changes in their molecular condition, it 
would appear that chemical action, and heat, and 
mechanical force, should be mutually convertible. This 
is now a widely recognized truth. 

Chemical changes are always attended by a change 
in the thermal conditions of the bodies acted upon, in 
which combinations as a rule, produce heat, while 
decompositions produce cold, or a disappearance of heat. 
The amount of heat any particular body is capable of 
giving off must be determined, as yet, experimentally. 
The researches of Favre and Silberman, Andrews, 
Thompson, Joule, and others, have given us a very close 
approximation to the dynamic value of heat, and the 
heating power of different fuels. The results of their 
investigations, so far as it affects the combustion of coal, 
are given elsewhere in this volume. 

Relation of Atomic Weights to Specific Heat — In regard 
to the atomic weights and their relation to specific heat, 
it is a noteworthy fact, that as the specific heat increases 
the atomic weight diminishes, and vice versa; so that the 
product of the atomic weight and specific heat is, in 
almost all cases, a sensible constant quantity (30). The 
most important experiments on the specific heat of elas- 
tic fluids we owe to M. Regnault. He determined the 
quantities of heat necessary to raise equal volumes of 
them, through the same number of degrees. Calling 
the specific heat of water 1, here are some of the 
results of this invaluable investigation : 



RELATION OF ATOMIC WEIGHTS TO SPECIFIC HEATS. 197 



Table XXIII. 
Specific Heat of Simple Gases. 



SPECIFIC HEATS. 



EQUAL 
WEIGHTS. 



EQUAL 
VOLUME! 



Air 

Oxygen... 
Nitrogen.. 
Hydrogen 
Chlorine- 
Bromine.. 



0.237 
0.218 
0.244 
3.409 
0.121 
0.055 



0.240 
0.237 
0.236 
0.296 
0.304 



We have already arrived at the conclusion that, for 
equal weights, hydrogen would be found to possess six- 
teen times the amount of heat possessed by oxygen, and 
fourteen times that of nitrogen, because the hydrogen 
contains sixteen times the number of atoms, in one case, 
and fourteen times the number in the other. We here 
find this conclusion verified experimentally. Equal 
volumes, moreover, of all these gases contain the same 
number of atoms, and hence we should infer that the 
specific heats of equal volumes ought to be equal. They 
are nearly so for oxygen, nitrogen and hydrogen ; but 
chlorine and bromine differ considerably from the other 
elementary gases. 

Table XXIV on the next page shows the specific 
heat of the elementary substances in table II, together 
with their atomic weights and products, the gases in 
table XXIII excepted : 



198 



COMBUSTION OF COAL. 



Table XXIV. 



Aluminum 

Calcium 

Carbon (charcoal).. 

Iron 

Magnesium 

Phosphorus 

Potassium 

Silicon (crystalized) 
Sulphur ...... 



SYMBOL. 


SPECIFIC 
HEiiJT. 


ATOMTC 
WEIGHT. 


Al 
Ca 


0.2143 

0.1670 


27.5 
40 


C 


0.2415 


12. 


Fe 


0.1138 


56 


Mg 


0.2499 


24 


P 


0.1887 


31 


K 


0.1696 


39 


8 


0.1774 
0.1776 


28 
32 



PR0I>trCT3. 



5.89 
6.68 
2.90 
6.37 
6.00 
5.85 
6.61 
4.97 
5.68 



It will be observed, In examining the column of pro- 
ducts formed by multiplying the specific heat and the 
atomic weights together, that there is a very close 
approximation to a constant product. Neglecting car- 
bon and silicon, which are, apparently, exceptions — 
and this may in part be accounted for, as they are so 
diverse in their known or ordinary physical conditions, 
they have not, in general, the uniform type of conditions 
which are so characteristic of most of the other ele- 
ments — aside from these, we find the lowest in this table 
to be 5.68, and the highest 6.61, making an average of 
6.07. 

If we were to obtain an average of all the products 
so far as known, it will be found to closely approximate 
6.34. This is too close to be accidental, and the usual 
explanation is (3), that the atoms of the different ele- 



SPECIFIC HEAT. 199 



merits have the same capacity for heat, and hence, that 
masses of the elementary substances containing the same 
number of atoms, must have the same capacity for heat 
when under similar physical conditions ; the constant 
product being the amount of heat required to raise the 
temperature of such masses to the same degree. 

Specific Heat — The specific heat of a substance 
means the quantity of heat, expressed in thermal units, 
which must be transferred to or from a unit of weight 
(such as a pound) of a given substance, in order to raise 
or lower its temperature, by one degree, at a certain 
specific temperature. 

According to the definition of a thermal unit, the 
specific heat of liquid water, at and near its temperature 
of maximum density, is unity ; and the specific heat of 
any other substance, or of water at any other part of 
the scale of temperatures, is the ratio of the weight of 
water at or near 39.1° Fahr., which has its temperature 
altered one degree by the transfer of a given quantity of heat, 
h the weight of the other substance under consideration, which 
has its temperature altered one degree by the transfer of an 
equal quantity of heat (22). 

The specific heat of a substance is sometimes called 
its " capacity for heat" 

The specific heats of water in the solid, liquid and 
gaseous state, are as follows : 

Ice 0.504 

Water 1.000 

Gaseous steam 0.622 



200 COMBUSTION OF COAL. 

showing that, in the solid state, as ice, the specific heat 
of water is only. half that of liquid water; and that, in 
the gaseous state, it is little more than that of ice, or 
nearly five-eighths that of liquid water. 

Table XXV. 
Specific Heat of Fuels. (After Regnault.) 



WATER AT 

32°=1. 



Oak wood ' .570 

Wood charcoal ' .2415 

Coal and coke, average (Rankine) 200 

Coke of cannel coal 20307 

Anthracite coal, Welsh .20172 

Anthracite coal. American ' .201 

I 

For all ordinary calculations it is a near enough 
approximation to assume that 

Woods average one-half the specific heat of water. 
Coal and coke, two-tenths the specific heat of water. 
"Wood charcoal, one-fourth the specific heat of water. 

Note — Slight fractional differences will doubtless be observed in the specific 
heats of the same substances. These have been calculated by different observers 
widely separated, and are really marvels of accuracy, notwithstanding the differences, 
which are so slight as to cause no material error in any calculation. B. 



LATENT HEAT. 



201 



Table XXVI. 
Showing the Specific Heat of Gases — Water at 32° Fahr = 1. 



Carbonic acid 

Oxygen 

Air 

Nitrogen 

Carbonic oxide 

Olefiant gas 

Hydrogen 

Vapor of alcohol 

Gaseous steam 

Light carbureted hydrogen 



SPECIFIC HEAT FOR 
EQUAL WEIGHTS. 



AT 
CONSTANT 
PRESSURE. 



0.2164 
0.2182 
0.2377 
0.2440 
0.2479 
0.3694 
3.4046 
0.4513 
0.4750 
0.5929 



AT 
CONSTANT 
VOLUME. 

(REAL 
SPECIFIC 
HEAT.) 



WATER=1 

0.1714 
0.1559 
0.1688 
0.1740 
0.1768 
0.2992 
2.4096 
0.4124 
0.3643 
0.4683 



SPECIFIC HEAT FOR 
EQUAL VOLUMES. 



AT 
CONSTANT 
PRESSURE. 



AIR=.2377 
AS IN COL. 2 

0.3308 
0.2412 
0.2377 
0.2370 
0.2399 
0.3572 
0.2356 
0.717.1 
0.2950 
0.3277 



AT 
CONSTANT 
VOLUME. 



AIR=.1688 
AS IN COL. 3 

0.2620 
0.1723 
0.1688 
0.1690 
0.1711 
0.2893 
0.1667 
0.6553 
0.2262 
0.2588 



Latent Heat — Is that quantity of heat which disap- 
pears, or becomes concealed in a body while producing 
some change in it other than a rise in temperature. By 
exactly reversing that change, the quantity of heat 
which had disappeared is re-produced. 

If heat is applied to a block of ice, having a temper- 
ature, say, ten or fifteen degrees below the freezing point 
of water, the temperature will continue to rise with each 
increment of heat until 32° Fahr. is reached, when the 
melting of the ice will begin ; it will be observed that 



202 COMBUSTION OF COAL. 

the heat being transmitted to the ice, as before, there is 
no corresponding rise in temperature, either in the ice 
or the water in contact with it, so long as any ice 
remains unmelted ; and, that during the process of melt- 
ing the temperature of the water is constant, and at 32° 
Fahr. 

Latent Heat of Fusion — This change of state from 
solid to liquid, in the melting of ice, requires one hun- 
dred and forty-three units of heat, the temperature 
being 32° as at first; the heat in this case does not raise 
the temperature of the ice, but disappears in causing its 
condition to change from the solid to the liquid state. 
According to our present theory (30), the heat expended 
in melting is consumed in conferring potential energy 
upon the atoms. It is, virtually, the lifting of a weight. 
The act of liquefaction consists of interior work — of 
work expended in moving the atoms into new positions. 
This is called the latent heat of fusion. 

Latent Heat of Evaporation — After the ice, in the 
above experiment, has entirely disappeared, the applica- 
tion of heat being continued, the thermometer will begin, 
and will continue to rise until 212° Fahr. is reached, 
when it again becomes stationary, and will remain so 
as long as evaporation is continued at atmospheric 
pressure. 

Again, it will be observed that heat disappears in 
the change of the water from the liquid to the gaseous 
state. Experimentally this has been ascertained to be 
nine hundred and sixty-six units of heat. From the 



MECHANICAL THEORY OF HEAT. 203 

freezing to the boiling point there are 212 — 32 = 180°; 
so we find that 966 -=-180 = 5.37 times as much heat 
is required to convert water into steam, at atmos- 
pheric pressure, as it requires to raise the temper- 
ature from the freezing to the boiling point. In the 
preceding section, the theory was given that the heat 
expended in melting the ice was consumed in conferring 
potential energy upon the atoms. In regard to the 
steam, or the evaporation of the water, the heat is con- 
sumed in pulling the liquid molecules asunder, confer- 
ring upon them still greater potential energy. 

When the heat is withdrawn, the vapor condenses, 
the molecules clash with a dynamic energy, equal to 
that which was employed to separate them, and the 
precise quantity of heat then consumed re-appears (30). 
The act of vaporization is, for the most part, interior 
work; to which, however, must be added the exterior 
work of forcing back the atmosphere, when the liquid 
becomes vapor. 

Mechanical Theory oe Heat — Professor Rankine's 
statement of the first law of thermodynamics is that, 

"Heat and mechanical energy are mutually convertible; 
and heat requires for its production, and produces by its dis- 
appearance, mechanical energy in the proportion of 772 foot- 
pounds for each British unit of heat: the said unit being 
the amount of heat required to raise the temperature of 
one pound of liquid water by one degree Fahrenheit, 
near the temperature of the maximum density of 
water" (22). 



204 COMBUSTION OF COAL. 

This is also known as the dynamical theory of 
heat. The 772 foot-pounds as the mechanical equiva- 
lent of a heat unit, is often referred to as Joule's equiv- 
alent, and is so called in honor of Dr. Joule, of Man- 
chester, England, who was the first to demonstrate 
experimentally the exact mechanical equivalent of heat. 
This honor Dr. Joule shares with Dr. Mayer, a physi- 
cian in Heilbronn, Germany. The relations of these 
two men to the mechanical theory of heat is thus 
expressed by Professor Tyndall : 

" The immortal investigations, here briefly referred 
to, place Dr. Joule in the foremost rank of physical 
philosophers. Mayer's labors have, in some measure, 
the stamp of a profound intuition, which rose, however, 
to the energy of undoubting conviction in the author's 
mind. Joule's labors, on the contrary, are an experi- 
mental demonstration. Mayer thought his theory out, 
and rose to its grandest applications ; Joule worked his 
theory out, and gave it forever the solidity of demon- 
strated truth. True to the speculative instinct of his 
country, Mayer drew large and weighty conclusions 
from slender premises; while the Englishman aimed, 
above all things, at the firm establishment of facts. The 
future historian of science will not, I think, place these 
men in antagonism. To each belongs a reputation 
which will not quickly fade, for the share he has 
ad, not only in establishing the dynamical theory of 
heat, but also in leading the way toward a right 
appreciation of the general energies of the universe." 



MECHANICAL THEORY OF HEAT. 



205 



The apparatus employed by Dr. Joule, in the deter- 
mination of this important constant, is represented in 
figure 7. A known weight was connected by means 
of cords to a shaft /, mounted on " friction-wheels," 
not shown in the cut ; on this shaft a pully was secured, 
and through the medium of another cord imparted 
motion to the shaft r, and caused it to revolve ; at the 
lower end of this shaft r, were fitted eight sets of pad- 
dles, which, when connected by means of a pin P, 




Figure 7. 



revolved with it. To the interior of the copper vessel 
B were attached four stationary vanes, cut out in such 
manner as to permit the free revolution of the revolving 
paddles. Precautions were taken to prevent a transfer 
of heat from the vessel B, which need not be described 
here. This vessel was filled with a known weight of 
water, at the temperature of its greatest density (39° 
Fahr.), and a thermometer t, was inserted in the vessel 
B, to mark the rise in the temperature of the water. 



206 COMBUSTION OF COAL. 

The experiment consisted in allowing the weight to 
descend by its own gravity, and through the medium of 
the cords to cause the paddles to revolve and agitate the 
water in the vessel B. 

Acting on the assumption that wherever there is 
motion there must he an evolution of heat, it was 
expected that, a weight falling through a certain dis- 
tance must occasion a certain rise in temperature in a 
certain weight of water, this was found to he true ; and 
after many hundreds of experiments, extending through 
several years, it was finally fixed by Dr. Joule at 772 
pounds raised one foot high against the action of grav- 
ity, as the mechanical equivalent of the quantity of heat 
necessary to raise the temperature of one pound of 
water through one degree at its temperature of maxi- 
mum density, or, from 39 to 40 Fahrenheit. 

The following are the values of Joule's equivalent 
for different thermometric scales, and in French and 
British units : 

One British thermal unit, or one degree Fahrenheit in one 
pound of water = 772 foot-pounds. 

One French thermal unit, or one degree Centigrade in one 
kilogramme of water = 423.55 (say 424) kilogrammetres. 

One degree Centigrade in one pound of water = 1389.6, or very 
nearly 1390 foot-pounds. 

One calorie, or French thermal unit = 3.968 British heat units. 

One British heat unit= .252 calorie. 

Unit of Heat — This is a conventional term express- 
ing the quantity of heat required to raise the tempera- 
ture of one gram of water from 4° to 5° Centigrade. 



UNIT OF HEAT. 207 



This is the French unit, and that principally used 
by chemists and scientific writers; it is sometimes 
spoken of as a calorie. 

The unit in more general use among English and 
American engineers is the quantity of heat required to 
raise the temperature of one pound of water from 39° 
to 40° Fahr. This is the unit selected for use in this 
hook. 

A thermal unit and a unit of heat mean the same 
thing. The use of the word calorie should never he 
considered a synonym for, and should not he used to 
express an English unit, hut should he referred to only 
as the French unit. 

Many writers, inadvertantly perhaps, give the unit 
of heat as that necessary to raise one gram of water 
from 0° to 1° Cent., or one pound from 32° to 33° Fahr. 
This is an error; it is the raising of the temperature of 
water through one degree at its temperature of greatest 
density: this on the Centigrade thermometer is 3°.94, 
or 39.1° Fahr. 

It will he near enough, however, for all practical 
purposes, to call the temperature of greatest density of 
water 4° Cent., or 39° Fahr. 



CHAPTER XL 

THE CONSTRUCTION OF FURNACES. 

Construction Depends on the Fuel — Conditions Attached to a Good 
Furnace — Why Ordinary Furnaces are so Wasteful — Volatiliza- 
tion of Gases in the Furnace — Quantity of Air Required — 
Force Blast — Description of a Reverberatory Furnace — Its 
Advantages— Increase of Efficiency by the Use of Hot Air — 
Loss by Chimney Draft. 

This chapter is made up of selections from a paper 
read before the " Edinburgh and Lieth's Engineers' 
Society," by Mr. Charles Fairbairn, a prominent manu- 
facturer of iron, who has given this subject a great deal 
of personal attention. 

His views are based upon correct theory, and con- 
firmed by actual trial. 

It is probable that much the same method of econo- 
mizing fuel, as that suggested by Mr. Fairbairn, will 
sooner or later be largely employed in steam boiler 
furnaces; by this, is meant, the generating of an intense 
heat, . and in large quantities, in a separate chamber, 
instead of directly under the boiler. The coal will 
probably be fed from underneath the lire ; that is, the 
blast will pass through the fresh charge of coal in some 
manner analogous to that shown in the engraving of Mr. 
Fairbairn's furnace; with any such arrangement as this, a 
force draft becomes a necessity; and by the use of a 
heated blast, instead of a cold one, a much higher 



• CONSTRUCTION OF FURNACES. 209 

degree of economy may be reached than is possible by 
ordinary firing, and natural draft. 

" The great variety of kinds of fuel, although they 
contain nearly the same ingredients, but in different 
proportions, renders it a somewhat difficult task to 
define what a furnace should be. Hydrocarbons, such 
as pitch, tar, naptha and petroleum, have all to pass 
into the gaseous state before they can be burned. 

"Coke, which is coal, with all the bituminous and 
gaseous portions taken out of it, is nearly pure carbon, 
with a small proportion of ash. 

"Anthracite coal, which is very similar in its nature 
to coke, is wholly composed of free carbon. It is liable 
to split and fall into powder;* it burns without flame,, 
and very little smoke, and requires a very strong 
draught. 

"Bituminous coal, again, of which there is am 
immense variety, has a smaller proportion „ of carbon,, 
with a mixture of hydrogen and oxygen. From this it 
will appear evident that special provision must be made 
for a supply of air to support combustion instead of the 
different kinds of fuel used. Thus, a furnace arranged 
for burning bituminous coal might be very wasteful in 
burning anthracite coal ; due regard then must be paid 
in all cases to the character of the fuel employed. 

The indispensable conditions attached to a good 
furnace, for all kinds of fuel, are, 

1. A good draft, which can be regulated at will, so 
as to avoid forcing the fire too much. 

^This remark does not apply to American anthracites. B. 

(15) 



210 COMBUSTION OF COAL. 

2. A large and roomy combustion chamber, sur- 
rounded by fire bricks, and removed, if possible, from 
the place where the heat is to be used. 

3. That the sides, or walls of a furnace, have at least 
ten thicknesses of bricks nearest the fire, and an outer 
wall having an air space between of about three inches. 

4. That the supply of air to the furnace can be 
regulated at will. 

"I do not think we can always command these con- 
ditions, especially in a furnace constructed on the prin- 
ciple of depending on atmospheric pressure for draught ; 
and the reason is obvious, because in order to obtain a 
good and equal draught we require not only a tall 
chimney, but the chimney must be maintained at a high 
temperature, about six hundred degrees; and as the 
temperature within the furnace may be assumed at 
twenty-five hundred degrees, the abstraction of this 
large quantity of heat to keep the chimney at a suffici- 
ently high temperature, amounts to one-fourth of the 
heat, and consequently of the fuel which is expended for 
that purpose alone. Nor is this the only drawback. 
The attendant on the furnace, who may, and often has 
other duties to perform, puts on a heavy load of coal. 
The flues and chimney are rapidly cooled, and the power 
of the draught reduced at the very time when it should 
be greatest. 

"The second and third conditions mentioned may 
assist in getting over irregularity in the power of the 
draught to a certain extent — that is, a large and roomy 



CONSTRUCTION OF FURNACES. 211 

combustion chamber, and the sides constructed to pre- 
vent loss of heat. 

"I do not suppose any person who has not had an 
opportunity of seeing a furnace in operation, with the 
heat confined in the manner described, could have 
believed the effect would be so powerful; the inner 
lining actually acquires a white heat, thus serving as an 
accumulator, which is given out again when the temper- 
ature of the fire is reduced (as in the case of a fresh 
charge of fuel), and at the same time assisting to bring 
the fresh fuel into active combustion more rapidly ; the 
heat is again returned to the fire bricks, and kept ready 
for future use. Dr. Siemens has taken advantage of 
this idea, although in quite a different way, in his cele- 
brated gas furnace. 

" We will now consider our furnaces as at present 
constructed, and why they are so wasteful. We hear a 
great deal about thin fires and regular charges in the 
ordinary; and this is quite correct, inasmuch as it is the 
only way by which a right supply of air can be intro- 
duced to mix with and consume the gases. There are 
always two dangers we have to avoid: One is too 
much air, which is the least of the evils, and in which 
case a very large body of air passes away unconsumed, 
but it also carries away with it a certain amount of heat 
which cools the furnace and impedes the draught. The 
other evil of too little air is still more injurious, for the 
gases having only a small share of the oxygen required are 
burned into c.irbonic oxide, and this very often accounts 
for the deficient supply of steam from a boiler, in con- 



212 COMBUSTION OF COAL. 

sideration of the coal burned. But these fires are liable 
to burn into holes and admit streams of cold air; nor is 
this the only objection, for when the fire is fed with fresh 
coal, which must of necessity- be very often, the new 
coal absorbs a large proportion of the heat of a thin 
fire, and immediately lowers the temperature. 

" The fire contains a certain number of units of heat. 
If twice the quantity of coal was in active combustion, 
there would be double the number of units of heat, and 
it could therefore more easily sustain the reduction of 
temperature following a fresh charge of coal. I imag- 
ine the distillation of gas from coal or volatilization is a 
process similar to steam carrying off the heat from 
boiling water. The coal at first becomes an absorbant 
of the heat and then liberates the gases, and the vola- 
tilization of the bituminous portion of the coal acts in 
a similar manner to the production of steam, as I have 
said. The process is one of the most energetic known 
in cooling, because there is so large a portion of the. 
heat converted from the sensible to the latent state. 

"Regarding the quantity of air required in an ordi- 
nary furnace for the combustion of coal, I suppose very 
few people have any idea of the magnitude of the 
demand. 

"It is generally given as 300 cubic feet, or 24 pounds 
of air to one pound of coal. Let us place this in 
another light : 

"In my own establishment at Gateshead I have seven 
furnaces, each of which uses about one ton of fuel per 
day, in all about seven tons; therefore 7X24 = 168 tons 



CONSTRUCTION OP FURNACES. 



213 



of air required. Again, a pound of coal requires about 
300 cubic feet of air. If we imagine the 168 tons of 
air made into a long stream of one square foot in area, 
the total length will be 21,381 miles in length. Another 
great cause of the loss of heat, as before stated, is the 
quantity of heat continually passing away to the chim- 
ney. 




Figure 



"One difficulty — that is, regulating the supply of air 
to the furnace — can only be overcome by artificial 
means, either by a fan-blast or steam-jet. I believe the 
time is fast approaching when the supply of air to 
furnaces will be regulated in this way, as the most 
efficient and economical, and as obviating a great many 
of the faults of our present furnace. 

" The idea is old enough. However, the arrangement 
of the furnace, I will describe presently, may or may 
not be new. I never saw it before, nor am I aware that 
anything of the same kind has been tried, and to it 1 
have added a supply of air by means of a blower. In 
this furnace, of which the drawing is a longitudinal 



214 COMBUSTION OF COAL. 

section, the coal is introduced from the top, and is 
always on top of the incandescent fuel, at the side of 
the furnace furthest from the place where the flame 
makes its escape. 

" The hearth is of fire-brick, and during the meal 
hours all the ashes and clinkers are removed by the 
hole in the side of the furnace. 

"The blast is introduced above the new coals, and 
passes through them. As the coals begin to ignite, all 
the inflammable gases are forced through the fire, and at 
the same time mixed with air. 

" The advantages with this kind of furnaces seem to 
be the following: 

1. The whole of the gaseous products are made 
available. 

2. There is entire absence of smoke, in consequence 
of perfect combustion. 

3. There is a smaller quantity of air required, prob- 
ably about one-fourth less; that is, about eighteen 
pounds of air to one pound of coal. 

4. No increase of temperature above the external 
air is required in the chimney, and the escaping heat 
from the furnace can be used for other purposes. 

5. A higher temperature in the furnace, and more 
rapid circulation of heat. 

6. The perfect control which the attendant has 
over the furnace as regards temperature, getting the 
fire lighted and into operation in less time, when they 
have not been in use. 



CONSTRUCTION OF FURNACES. 215 

" There is also another very important point in con- 
nection with this method of making re-heating fur- 
naces — that the air can be so nicely adjusted by means 
of the blast and damper, as to insure that nearly all the 
oxygen will be taken up by the carbon and gases, in 
consequence of which the iron is heated with scarcely 
any loss from oxide or scale.* The balance of pressure 
can be made so that even where there are unprotected 
inlets to the interior of the furnace, the flame can be 
made to come to the edge of the open space. I believe 
the efficiency of the furnace might be largely increased 
by using hot air, which might be done by passing it 
through pipes or brick work placed in the flues; for if 
we have the heat of the furnace twenty-five hundred 
degrees, and the entering air heated to five hundred 
degrees, the result would necessarily be a great saving. 
On this point we have the experiences of blast furnaces 
as an indication of what might be saved by this means 
alone. 

I have again to mention that a furnace, which will 
suit admirably for one kind of coal, will not answer for 
another. Thus, the conditions under which coke and 
anthracite coal enter into combination with oxygen, are 
much less complex than in burning bituminous coal, 
and the great point to be observed is, that a large quan- 
tity be kept on the bars ; there is not so much danger 
of the carbon passing away without its supply of 
oxygen — in fact it can not do so, as it can not rise until 

-The reader will of course understand that the engraving is a section of, and the 
heating of the iron refers to a puddling furnace. B. 



216 COMBUSTION OF COAL. 

it has its quantity of oxygen to liberate it. In bitumin- 
ous coal the bituminous portion is only serviceable for 
heat when converted into gas, while the carbonaceous 
portions are consumed only in the solid state, and they 
must be separated, as explained, before they can be 
consumed. Thus, when coke or anthracite coal are 
burned, the products are carbonic acid gas, and nitro- 
gen ; while with bituminous coal we have carbureted 
hydrogen, nitrogen and carbonic acid gas, or oxide. 

"It is supposed that in some instances we have real- 
ized about seventy per cent, of the theoretical heat in 
fuel. This, I would be inclined to doubt. "We have 
seen that with the ordinary furnace we lose about 
twenty-five per cent, in getting a draught; we have to 
add to this loss from small coal, too much or too little 
air; the products of combustion flying off to the chim- 
ney at a speed of thirty feet in a second in some 
instances, it must be abundantly clear that fifty per 
cent, of the heat of fuel we use is lost. It has been 
stated that, in some processes in connection with 
the manufacture of iron, the quantity of fuel used 
was sufficient to produce the desired result four- 
teen times if properly applied. I think it is clear we 
begin by placing the chimney at the wrong end of the 
furnace, and the air ought to be driven in, not drawn 
through. We have seen when a blast is used we can 
have a pressure in the furnace sufficient to balance the 
pressure of the atmosphere. The waste heat could also 
be made to do work in passing away. I dare say most 
of us now present can recall instances to our mind 



CONSTRUCTION OF FURNACES. 217 

where a number of furnaces are used, and where the 
heat of one, if it could be retained and applied, would 
be amply sufficient. 

"The blast, then, is the only means of doing it, and 
I do not think the time is far distant when the hideous 
pillars we seem so fond of now will be no longer seen.' 5 



CHAPTER XII. 

MECHANICAL FIKING. 

Objections to Hand Firing — Continuous Firing — The Eequirements 
of a Self-feeding Mechanism — Description of M. Holroyd 
Smith's Furnace-Feeder. 

There are several objections to hand-firing, when 
taken in connection with steam boiler furnaces. In 
order to get the best results from such a furnace the 
firing should be as nearly constant as possible, in order 
that chemical action may go on undisturbed. Hand 
firing must, from its nature, be intermittent, and there- 
fore irregular. When the fire is brisk, and a boiler 
steaming rapidly, the opening of the furnace doors in 
order to admit a fresh charge of fuel, and thus allowing 
a draft of cold air, often below the freezing point of 
water, to impinge against the heated plates of the 
boiler, at the same time lowering the temperature of 
the gases in the furnace, and added to this, the deaden- 
ing of a brisk fire by a fresh charge of coal, always in 
excess of actual requirements, and too often unevenly 
spread, is certainly not conducive to the highest 
economy. 

The advantages of continuous firing were pointed 
out early in the present century, and a great number of 
devices have been tried from time to time, many of 
which have long since disappeared to give place to better 
contrivances to this end. 



MECHANICAL FIRING. 219 



The ideal mechanism for feeding steam boiler fur- 
naces, must, in addition to supplying the fuel, distribute 
it in such manner that it may be economically burned ; 
it must admit a proper supply of air at the right time 
and place to insure perfect combustion, and prevent 
smoke ; it should be adapted to the use of line or slack 
coal, and preferably, granular fuel; it should be so 
arranged as to admit of a forced draft being used ; it 
should admit the examination of the fire at all times, 
and the stirring or slicing of it whenever needed; it 
must permit the ready removal of clinker from the grate 
bars as fast as it accumulates; it must permit the ready 
removal of ashes from the fire, while in actual operation, 
without breaking it up, or destroying its efficiency; the 
parts should be few and free from complications; all 
moving mechanism should be protected from the heat 
and action of the fire; it should consist of parts easily 
made and repaired; and, as a whole, must combine 
utility, simplicity, economy, ease of management and 
durability. 

The furnace-feeder, described below, was devised by 
Mr. M. Holroyd Smith, of England, and appears to 
combine most of the requirements enumerated above ; 
and, in addition, it will be observed that the coal is 
forced into the fire from underneath, so that the volatile 
gases are extracted by the incandescent fuel above it, 
and burnt as fast as evolved from the fresh supplies. 
There are many other forms of furnace-feeders in use, 
and doing good service. 



220 COMBUSTION OF COAL. 



M. HOLROYD SMITH'S FURNACE FEEDER.* 

"This invention relates to improved apparatus for 
supplying the fuel by self-acting mechanism, designed 
to supply the fuel from underneath the fire, the object 
being to insure more complete combustion, and, as a 
consequence, increased economy of fuel. 

"This invention relates to an improved apparatus for 
feeding fuel to the grate of a furnace; and consists in 
combining the grate-bars of the furnace with troughs 
or screw-cases, that are placed between and communi- 
cate with the grate-bars, and are connected at one end 
to a feed-trough and a hopper, said screw-cases contain- 
ing each a screw or worm, all being so arranged that 
the fuel is fed by the screws or worms from the hopper 
and feed-trough into the screw-cases, and from the 
screw-cases directly upon the grate-bars, all as is here- 
inafter more fully described. The screw has, by prefer- 
ence, two threads of such pitch and construction as to 
exert an outward and a propelling force. The propell- 
ing force of the screw at its commencement is in excess 
of its lifting force; but at its smaller end the lifting 
force is greatest, thereby insuring a uniform feed the 
whole length of the bars. 

"I prefer to use my improved feed mechanism in 
connection with improved supplementary or auxiliary 
back grids or grates (placed off the ends of the furnace- 
bars) and apparatus for operating the same, so as to 
remove the spent fuel or ashes therefrom. 

♦Patented January 8, 1878. 



M. HOLROYD SMITH'S FURNACE FEEDER. 221 

" The auxiliary bars I mount on axles within a frame, 
and the bars are connected by a link-motion that, by 
working a "draw" or "push" rod, the bars will tilt and 
throw off the ashes or spent fuel delivered on them 
from the main fire-bars. 

"The several parts will be clearly understood by 
reference to the drawings, aided by the description 
annexed. 

" Figure 1 is a longitudinal elevation, partly in section, 
illustrating my invention applied to an internally-fired 
single-flue steam-boiler. Figure 2 is a plan of the same. 
Figure 3 is an elevation in cross-section, on line a b of 
figure 2, of some of the parts of the apparatus. Figure 
4 is a front or outside elevation. Figure 5 is a plan 
view, enlarged scale, showing more clearly the screws 
and screw-case, the latter in section. 

" Similar letters of reference indicate corresponding 
parts in all the figures. 

u A A A are taper screws or worms; B B B, the 
screw-cases, connected at the front of the boiler by the 
feed-trough C, the latter being supplied with fuel by 
way of the hopper E. The screws AAA are supported 
at one end by the feed-trough C, and by contact with 
the bottom of the screw-case. 

" Motion is given to the screws A A A by means of 
the ratchet-wheels F F F and pawls, linked together 
by bar G, and actuated by lever H; or the three worms 
A A A may be driven by longitudinal shaft-worm and 
worm-wheels. 



222 COMBUSTION OF COAL. 

",/is a frame, within which the auxiliary bars K are 
received, being free to tilt on their axles or gudgeons L 
when, by means of the rod M, the links N R R are 
operated, so as to tilt and thereby discharge the ashes or 
spent fuel from the bars to the bottom of the flue. 

" Two screws may be put in one screw-case. 

"I do not claim as my invention the use of a screw 
per se; but 

"I claim — 

"The combination of the grate-bars of a furnace 
with the troughs or tapering screw-cases B B, that are 
placed below and between, and communicate with the 
several grate-bars, and connect at one end to a hopper, 
each of said screw-cases containing a tapering screw or 
worm, A, so arranged that the fuel is fed by the screws 
or worms A from the hopper into the screw-cases B, 
and from the screw-cases directly upon the grate-bars, 
all substantially as and for the purpose herein shown 
and described." 



M.H.SMITH. 
FURNACE FEEDER 







FIG. t 










■f 






~C ' 


25Sjg 






















Eammastxin "Bros 6 Co. L>Hi Jndtanapolisjni.. 



CHAPTER XIII. 



SPONTANEOUS COMBUSTION OF COAL.* 

Most Likely to Occur on Board Ships — Vessels Lost from this 
Cause in 1874 — Spontaneous Combustion Begins in the Center 
of the Heap or Middle of the Cargo — Iron Pyrites in Coal 
— How Carbon Spontaneously Ignites — Coal requires no Initial 
Temperature for its Combustion — No Limit to the Heat which 
may be Produced by Concentration. 

" The most serious cases of spontaneous combustion 
are in ships carrying coal. These have of late been so 
numerous, and have so often occurred in despite of 
manifold precautions, that a royal commission was 
recently appointed to make inquiry into the causes of 
these terrible catastrophes, and to suggest remedies 
which it may be possible to adopt for preventing and 
guarding against them. Numerous board of trade 
inquiries had already been made into casualties caused 
by explosions or fires in coal-laden vessels, but without 
any improvement in the safety of shipment resulting 
therefrom, until, at length, the board declined to hold 
any more, for the reason that the findings of their 
courts (which invariably took the form of an exonera- 
tion of the ship's officers, and a recommendation in 
favor of better ventilation) appeared to be entirely dis- 
regarded, both by shipping and underwriting interests. 

"It was evident, from this state of things, that the 
coal shippers conceived that they knew more of the 

♦ Charles W. Vincent, F. E. S. E., F. C. S. 



224 COMBUSTION OF COAL. 

causes of these accidents than did the assessors of the 
hoard of trade. The Salvage Association thereupon 
urged that an inquiry should he held hy a commission, 
consisting of men of high scientific attainments, and 
especially acquainted with the nature of coal in all its 
conditions, and of men practically acquainted with coal, 
"both at the pit and in the ship's hold. They pointed 
out that the result might he to fix, with a certainty 
absolute or qualified, the causes of this dangerous 
combustion, thereby attaching to proper persons the 
responsibility for due precautions. 

" The commission sat, and has now issued its report, 
from which much valuable information as to the nature 
of these disasters can be obtained, and, to a certain 
extent, modes of preventing them, though this part of 
the subject still requires most serious consideration, 
since at present the carriage of coal for a long distance 
at sea must be regarded as hazardous, whatever precau- 
tions may be adopted. 

"At the commencement of the inquiry, they were 
struck by the circumstances that by far the greater part 
of the casualties happened on board ships which were 
on long voyages. In 1874, among thirty-one thousand, 
one hundred and sixteen shipments, amounting to 
upwards of thirteen million tons of coal, the accidents 
were seventy. But of these shipments, twenty-six 
thousand, amounting to over ten million tons, were to 
European ports. This left sixty casualties among only 
four thousand, four hundred and eighty-five shipments, 
amounting to two million, eight hundred and fifty-five 



SPONTANEOUS COMBUSTION OF COAL. 225 

thousand, eight hundred and thirty-one tons of coal, to 
Asia, Africa and America. 

"Again, they were startled to find that the propor- 
tion of casualties traceable to spontaneous combustion 
increases, pari passu, with the tonnage of the cargoes. 
This becomes still more apparent when the European 
trade is deducted. 

" There were in 1874— 

" Two thousand one hundred and nine shipments 
with cargoes under five hundred tons, in which five cas- 
ualties occurred, or under one-fourth per cent. 

" One thousand five hundred and one shipments,, 
with cargoes between five hundred tons and one thou- 
sand tons, in which seventeen casualties occurred, or- 
over one per cent. 

"Four hundred and ninety shipments, with cargoes 
between one thousand and one thousand five hundred' 
tons, in which seventeen -casualties occurred, or three, 
and a half per cent. 

" Three hundred and eight shipments, with cargoes- 
between one thousand five hundred and two thousand 
tons, in which fourteen casualties occurred, or over four 
and a half per cent. 

" Seventy-seven shipments, with cargoes over two 
thousand tons, in which seven casualties occurred, or 
nine per cent. 

"The casualties in vessels bound to San Francisco 
were the most remarkable. Deducting vessels under 
Hve hundred tons (in which no case of spontaneous 
(16) 



226 COMBUSTION OF COAL. 

combustion were recorded) the returns show nine cas- 
ualties out of fifty-four shipments. These also increase 
in proportion to the tonnage of the cargoes, till we find 
that, out of five ships with cargoes of over two thou- 
sand tons sent to San Francisco in 1872, two suffered. 

■" Careful thought might have predicted results of 
this kind from a consideration of the nature of the sub- 
stance carried, the mode of carriage, and the place to 
which it was going. 

" So long ago as 1852, Graham pointed out that the 
tendency of coals to spontaneous ignition is increased 
by a moderate heat, and gave examples. For instance, 
in one case coal had taken fire by being heaped for a 
length of time against a heated wall, the temperature of 
which could be easily borne by the hand; in another, 
coals ignited spontaneously after remaining for a few 
days upon stone flags covering a flue, of which the tem- 
perature never rose beyond 150° Fahr. Coals thrown 
over a steam-pipe ignited, etc. At the Chartered Gas 
Works, coals piled against a brick wall two feet thick, 
of which the temperature did not exceed 120° to 140° 
Fahr., became ignited. Neither did it appear to matter 
whether the coal was Lancashire and sulphurous, or 
Wallsend and bituminous. If they were exposed to 
this very moderate heat for a short time they were sure 
to ignite. 

" Coals conveyed through the tropics are certainly 
in this state of danger. When coal takes fire spon- 
taneously, it is invariably in the center of the heap of 
small coal at the foot of a hatchway, or in the middle of 



SPONTANEOUS COMBUSTION OF COAL. 227 

the cargo, in this respect resembling the spontaneous 
combustion of hay-stacks, oily waste, etc., and from 
hence it may be inferred that the increments of heat 
which cumulate in vivid combustion are very small, 
since they require to be held prisoners by impassable 
barriers of non-conducting matter, or they would escape. 

"Coal in small quantity, and in a cool place, never 
ignites spontaneously, but it does not, therefore, follow 
that all the conditions leading up to spontaneous com- 
bustion are absent, but only that one of them, and that 
an all -important one, the means of accumulating of 
heat, is absent, since the barriers interposed to its escape 
are not sufficiently close-fitting. 

" The large ships to San Francisco had to encounter 
elevated temperature, and at the same time the coal was 
in great mass; they were, therefore, much more liable 
to accident than those carrying smaller quantities, and 
for shorter distances. 

" It has already been pointed out that, whilst wood 
is living, moderate heat, so far from causing its destruc- 
tion, promotes its growth; it is the heat which disap- 
pears, not the plant. When the wood has ceased to 
live, moderate heat dries up its juices, renders it brittle, 
and ultimately causes its complete disintegration, and 
combustion of air is supplied, though the process is 
exceedingly slow. Some years ago, the sawdust pack- 
ing round a steam pipe at the Queen's Printing-office, 
Shackleweli, was found to be charred. Wooden beams 
resting against hot plates which never reach the boiling 
point of water, are sometimes found to be charred, but 



228 COMBUSTION OF COAL. 

oxygen being of necessity excluded by the position of 
the wood, combustion does not happen. 

"At the ordinary temperature of the air, oxygen has 
so little action upon wood that it is practically inde- 
structible. In coal, however, the wood has undergone 
changes which render it far more readily affected by the 
oxygen of the air than it was heretofore, and it must be 
borne in mind that if once a combustion is sufficiently 
rapid to overcome the cooling effect of currents of air, 
it will proceed with increased vigor, and the ignited 
coal will burn, not only in the interior of the cargo or 
heap, but on its surface also. Knowing, then, that coal, 
if kept in bulk at a temperature slightly raised above 
the common is sure to ignite, the question still remains, 
how does it attain the degree of heat at which active 
combination can take place ? And at what tempera- 
ture do the combinations of the carbon and oxygen, the 
hydrocarbons and the oxygen, begin to take place ? In 
other words, what is the temperature of the initial point 
of the combustion, and how is it reached? Many 
explanations have been given. The well-known fact 
that heaped-up iron pyrites in shale, when wetted, often 
causes the combustion of the pile, as in alum making, 
has been used as an argument against the shipment of 
"brassy" coal, i. e., coal containing these pyrites. But 
supposing this were so, and that the pyrites were dis- 
seminated through a part of the cargo in sufficient 
quantity to cause evolution of heat when wetted, this 
would account for but a small number of the cases of 



HOW CARBON SPONTANEOUSLY IGNITES. 229 

spontaneous combustion of coal, since by far the larger 
number happen with coal free from pyrites. 

HOW CARBON SPONTANEOUSLY IGNITES. 

"Condensation of oxygen, by carbon, which was 
referred to at the outset of this paper, is a far more 
likely mode of attaining the initial temperature. This 
is pointed out by Professor Abel and Professor Percy in 
the appendix to the report of the Royal Commission. 
As already stated, carbon, in a finely divided state, has 
the power of condensing oxygen within its pores; now, 
to condense a gas, force is consumed, and heat is pro- 
duced. In the fire-syringe a piece of tinder is set on 
fire by the heat evolved by the condensation of the air. 
When charcoal condenses oxygen, heat is liberated, and 
if the charcoal is freshly burned, the rapidity of the 
action will produce such an amount of heat as to cause 
the chemical combination of the oxygen and carbon, 
when, of course, combustion takes place with evolution 
of light and heat. The initial temperature of the action 
is here due to the sudden squeezing together of the 
gaseous molecules, for if the air be admitted to the 
freshly burned charcoal by slow degrees, no combustion 
takes place. 

" The appendix suggests : 

" ' The tendency to oxidation, which carbon and car- 
bon compounds, existing in such a substance as charcoal, 
possess, is favored by the condensation of oxygen within 
its pores, whereby the very intimate contact between 
the carbon and oxygen particles is promoted. Hence, 



230 COMBUSTION OF COAL. 

the development of heat, and the establishment of 
oxidation occur simultaneously, the latter is accelerated 
as the heat accumulates, and chemical action is thus 
promoted, and may, in course of time, proceed so ener- 
getically that the carbon or carbo-hydrogen particles 
may be heated to igniting point. 

" ' This explanation has a direct bearing upon a spon- 
taneous ignition of coal. The more porous and readily 
oxidizable portions of coal, which are known to be more 
or less largely disseminated through seams from different 
localities, undergo oxidation by absorption of atmos- 
pheric oxygen, and by the exposure of large surfaces to 
its action, and the heat developed by that action will 
accumulate, under favorable conditions, to such an 
extent as soon to hasten the oxidation and the conse- 
quent elevation of temperature, until some of the most 
finely divided and readily inflammable portions actually 
become ignited.' " 

" "Water does not assist in the spontaneous combus- 
tion of coal except where pyrites are concerned. There 
is much misunderstanding as to the part played by 
water in the changes leading to spontaneous combus- 
tion. The water itself is not decomposed, as some 
people have imagined. The heat evolved during the 
combustion of hydrogen and oxygen, during the com- 
bination to form water (the heat of the oxy-hydrogen 
blow-pipe) must be supplied before they can be again 
torn apart, so that, so far from water being a producer 
of heat, it is likely to be a consumer. 



HOW CARBON SPONTANEOUSLY IGNITES. 231 

"Moreover, experiment goes to prove that coal 
requires no initial temperature for its combustion, and 
that the supposition of condensation by porous coal, 
though it may take place, is unnecessary for its spon- 
taneous combustion. The ties holding the constituents 
of coal together, which in the living plant were so 
strong that they defied the power of the sun to rend 
them asunder, have now become so weak that the oxy- 
gen of the air, even when no hotter than fifty -five 
degrees Fahr., can seize upon and combine with at least 
some of the carbon, forming carbonic acid. Air blown 
through a tube filled with coarsely powdered coal, 
into baryta water, furnishes a considerable amount of 
barium carbonate in a very short time. Other circum- 
stances may aid, but it is sufficient to prove the produc- 
tion of carbonic acid to make it certain that heat is set 
free, and if escape of the heat is barred, it must accu- 
mulate, till at length it reaches the point at which com- 
bustion becomes visible, and in too many cases uncon- 
trollable. 

"As there is no amount of cold which may not be 
intensified by free radiation, so there is no limit to the 
heat which may be produced by concentration, or, in 
other words, by stoppage of all radiation except to one 
common point. Siemens' admirable regenerators act on 
the principal of continuous passage of heated gases 
through passages, where the gases are deprived of heat; 
when the heat producers go forth to do their work, 
they are first made to pass through these heated pass- 
ages. In addition to their own proper heat, they thus 



232 COMBUSTION OF COAL. 

convey forward the stored-up heat, and the most intense 
heat yet met with for practical purposes is attained. 

" It is to he feared that, in ventilating the cargoes of 
coal-ships, the principle of Siemens' regenerator is 
infringed upon, to the great damage of the cargo. Air 
is forced through the coal, oxidation and heat follow 
throughout its course, the heat is absorbed by the coal, 
and the air, as it is continuously forced in, passes over 
surfaces which are becoming hotter and hotter, the air 
is itself heated, and the work of combustion, once 
begun, goes on more and more rapidly. 

"In view of these facts, there is small wonder that 
the uniform recommendation of the Board of Trade 
Assessors, 'to ventilate the cargoes,' should have met 
with cavalier treatment. The subject is, however, yet 
far from being fully understood. Evidence has been 
collected from most trustworthy sources, and a clear 
understanding obtained of the various conditions under 
which spontaneous combustion of coal takes place. 
What is now wanted is, a thorough experimental inves- 
tigation of the causes of the spontaneous combustion. 
The reasons already given are probably correct, but 
they are supported by the feeblest experimental support, 
and until this is strengthened, we can neither speak 
with the necessary boldness in reproving the actions 
which lead to the lamentable losses of good fuel, good 
ships, and, but too often, of good men; nor can wo 
decide as to the proper means for preventing their 
occurrence." 



CHAPTER XIV. 

COAL-DUST FUEL. 

Continuous Firing — How a Furnace should be Fed when Using 
Powdered Fuel— Experiments of United States Government 
in 1876 — Comparative Economy of Powdered Fuel as Com- 
pared with Ordinary Coal — Stevenson's Apparatus for Burn- 
ing Coal- Dust. 

COAL-DUST FUEL (8). 

When coal is burned in large lumps a certain 
amount of power is expended in the furnace in disinte- 
grating the fuel. This is, however, comparatively a 
small matter. But it is obvious that difficulties are 
thrown in the way of the union of the carbon with the 
oxygen of the air, and it has come to be recognized as a 
feature of good stoking that the coal should be broken 
into moderately small pieces before it is put into the 
furnace, and that the process of firing should be as con- 
tinuous as possible. The great advantage derived from 
the use of mechanical stokers lies no doubt in the 
almost perfect fulfillment of the last named condition. 
If we carry the idea a little further, the use of coal in a 
state of powder will suggest itself; and as it is impossi- 
ble to feed a fire satisfactorily by hand with coal-dust, 
it has come to be understood that it should be blown 
into the furnace with the air required for its combus- 
tion, which is thus intimately mingled with the carbon. 
Until a very recent period this system was only used by 
Mr. Crampton, whose well known revolving puddling 



234 COMBUSTION OF COAL. 

furnace is supplied with powdered coal by a fan blast, 
the coal being first ground very fine between an ordin- 
ary pair of millstones. We believe that at one time 
Mr. Crampton applied this system, but without success, 
to a steam boiler. We are not in possession of any of 
the details of this experiment, and so we can say noth- 
ing about the cause of failure. 

UNITED STATES EXPERIMENTS. 

In 1876 a series of trials were conducted by the 
American Government to determine the value of a sys- 
tem of burning powdered fuel, patented by Messrs. 
Whelpley and Storer. 

The boiler was forty inches in diameter and ten feet 
long; it was a plain cylinder externally fired, the products 
of combustion returning to the front end through sev- 
enty-four tubes two and one-quarter inches in diameter 
outside ; the total heating was four hundred and forty- 
two square feet. The air required for combustion was 
delivered into the closed ash-pit, vertically, through a pipe 
five inches in diameter. The powdered coal was sent in 
through a pipe two inches in diameter, arranged hori- 
zontally. The boiler was tried both with powdered an- 
thracite and lump anthracite, the only change made as 
regards the boiler consisting in the removal of a brick 
arch used with the dust fuel. This increased the heating 
surface to four hundred and fifty-seven square feet. Each 
experiment lasted forty-eight hours. Four experiments 
were made; two with lump coal alone, and two with 
lump coal supplemented by dust coal below or above it. 



COAL-DUST FUEL. 235 



"Results of Experiments — Calling the experiments 
with lump coal alone A, and those with dust coal C 
and D, the results may he briefly stated as follows: 
In experiment A, 11.113 pounds of lump coal were 
consumed per hour per square foot of grate surface, 
with 80.478 double strokes of the piston of the engine 
supplying air; the resulting vaporization per pound of 
the combustible portion of the coal was 10.124 pounds 
of water from the temperature of two hundred and 
twelve degrees Fahrenheit, and under the atmospheric 
pressure. The mean rate of combustion in experi- 
ments C and D was 11.350 pounds of the combustible 
portion of the coal consumed per hour per square 
foot of grate surface, with 79.748 double strokes per 
minute of the piston of the engine supplying air, the 
resulting vaporization per pound of the combustible 
portion of the coal being 10.192 pounds of water from 
the temperature of two hundred and twelve degrees 
Fahrenheit, and under the atmospheric pressure. The 
two economic results — namely, 10.124 and 10.192 — are 
almost identical, and show, when semi-bituminous coal 
is burned at the same rate of combustion, with the same 
pro rota air admission, and under the same circum- 
stances, it gives the same economic vaporization, 
whether it is consumed wholly in the lump state, or 
partly in the lump and partly in the pulverized state, 
or wholly in the pulverized state. The equality of 
economic result is also proved by the fact of the 
equality of the temperature of the gases of combustion 
in the comparable experiments when leaving the boiler. 



236 COMBUSTION OF COAL. 

In experiment A, burning lump coal alone, this temper- 
ature was 383.30 degrees Fahrenheit, while the mean of 
the temperature of the gases of combustion in the 
boiler-uptake during experiments C and D, during 
which partly lump coal and partly pulverized coal 
were consumed, was 381.85 degrees Fahrenheit. This 
comparison is made, however, for the heating effects 
alone of the coal in the two states, burned under the 
same circumstances, and is exclusive of the cost in fuel 
of pulverizing the coal, and of blowing the dust into 
the furnace. A correct commercial comparison must 
include this cost, which is only incurred when the coal 
is used in the pulverized state, because when it is used 
in the lump state it can be burned as rapidly with the 
natural draught as the pulverized coal can with the 
artificial draught obtained by the fan-blowers. The 
reason why the pulverized coal can not be consumed at 
a greater rate with the fan-blowers than the lump coal 
can be consumed with the average draught given by 
the boiler chimney is, that the former requires a certain 
time for ignition and combustion, which is much longer 
than the latter requires, because the temperature to 
which the former is exposed above the bed of incandes- 
cent fuel on the grate-bars is much less than the tem- 
perature of that bed to which the latter is exposed. 

"The cost of the net horse-power in average practice 
may be taken at about four pounds of coal per hour. 
Now, the mean of experiments C and D gave 1.381 net 
horse-power developed by the engine in pulverizing the 
coal, and in blowing the dust into the furnace, and in 



COAL-DUST FUEL. 237 



pumping the feed- water into the tank, which, at four 
pounds of coal per hour per horse-power, is 5.524 
pounds of coal per hour, or, as the coal consumed per 
hour was 66 pounds, 8.37 per cent, of the total weight 
of coal burned. Consequently, the pulverized coal was 
commercially 8.37 per cent, inferior to the lump coal. 
In experiment A, during which lump coal was burned 
alone, there was required to drive the fan-blowers and 
to pump the feed-water 0.500 net horse power, which, at 
four pounds of coal per hour per horse-power, required 
2.000 pounds of coal per hour to produce it, and as the 
hourly consumption of coal during that experiment was 
66 pounds, there were consumed in producing the artifi- 
cial draught and in pumping the feed-water 3.06 per 
cent, of the total weight of coal burned. Deducting 
this 3.06 per cent, from the 8.37 per cent., as given in 
the immediately preceding paragraph, there remains 
5.31 per cent, of the total weight of coal consumed, 
applied to the pulverization of the coal alone. * 

"From this it will be seen that the use of powdered 
fuel was more expensive than that of lump coal, about 
in the ratio of the cost of pulverization, and so far the 
scheme was a failure. As regards the details of the 
apparatus used our information is meagre. Mr. B. F. 
Isherwood, by whom the experiment was made, thus 
comments on it : ' The lump coal is first reduced by a 
patented apparatus (which is the only portion of Messrs. 
Whelpley and Storer's process that is patented or patent- 

*Vide Annual Report of the Chief of the United States Bureau of Steam En- 
gineers for 1876. 



238 COMBUSTION OF COAL. 

able) to the state of impalpable powder, and it is then 
fed, together with air, through a conduit to the central 
portion of an ordinary centrifugal or fan-blower, whose 
revolutions draw it in and drive it through another 
conduit, which discharges it into the front of the furnace 
through an air-tight aperture. The lump coal is fired 
in the usual manner, through the furnace-door, and the 
air for its combustion is supplied by another fan-blower 
delivering into a closed ash-pit beneath the grate-bars. 
The whole combustion is, therefore, effected by artificial 
draught depending on mechanism; and the force of this 
draught is easily regulated from the least to the greatest 
desirable in burning coal; it can also be distributed at 
will, so as to preserve within certain limits any required 
proportion between the weights of lump and dust coal 
consumed in the same time. The two fan-blowers, in 
the experiments described, were operated by the same 
steam engine which effected the coal-crushing and 
worked the feed-pump of the boiler. 

Why the Experiments were made — " The patentees 
imagine that, compared with the combustion of lump 
coal, a more nearly perfect combustion was to be 
obtained with impalpably line coal-dust mixed throughly 
with and suspended in air, thereby presenting to the 
latter, for a given weight of coal, an immensely greater 
surface than in the lump state. They imagined, too, 
that, from the same cause, a much higher rate of com- 
bustion would be obtained than was probable with 
lump coal, by which means a boiler with a much smaller 
grate-surface, but with the same heating surface, would 



Stevenson's apparatus. 239 

furnish, with the coal-dust the same quantity of steam 
in equal time, and with greater economy of evaporation 
per pound of fuel than with the lump coal. It was to 
determine the truth or error of these assumptions that 
the experiments were made. They were intended to 
have been very extensive, embracing anthracite and 
coke, as well as bituminous and semi-bituminous coals; 
and also a species of exceedingly hard anthracite, found 
in Rhode Island, which contains about forty per centum 
of incombustible mineral matter, and is worthless, from 
its difficulty of ignition and slowness of combustion, for 
burning in lumps. The results from different rates of 
combustion and different proportions of dust, to lump 
coal consumed in equal time, were likewise to have 
been ascertained, but the experiments were prematurely 
closed, as the government could not longer dispense 
with the services of the naval engineers making them. 

"The obvious defects of the scheme were, that the 
coal could not be burned fast enough, and it is instruc- 
tive to note that the cooling down of the furnace of the 
boiler was one principal factor in bringing about this 
result," 

STEVENSON'S APrAEATUS. 

Plate IV is a representation of the apparatus for 
burning coal-dust, the invention of Mr. G. K. Stev- 
enson, of Valparaiso, and which has been at work in 
Wellington street, Blackfriars, London. This appara- 
tus overcomes, it would appear, the objections urged 
against Messrs. Whelpley and Storer's plan, and de- 
serves attention from engineers. The apparatus is 



240 COMBUSTION OF COAL. 

illustrated in the accompanying engravings, and may 
be briefly described as follows: The boiler used is 
one of two precisely alike, placed side by side, as 
shown. They are Cornish boilers, with a single flue 
in each, and are of the dimensions shown in the draw- 
ing. Contining our attention to that to which Mr. 
Stevenson's invention is affixed, it will be seen that the 
grate-bars are removed, and in the furnace is placed a 
species of fire-clay retort, the sides of which are perfor- 
ated with numerous holes, about a half inch in diam- 
eter. The air and powdered fuel are driven in together 
through the pipe B, which is six inches in diameter. A 
few fire-bricks are arranged in the flue, behind the 
retort, to act as a bridge.' 

"The coal is reduced to a fine powder by a small 
disintegrator, which delivers into a closed sheet iron 
tank to prevent the escape of dust. It is brought to 
the condition of a somewhat coarse powder, and is not 
impalpable. The appliances in use in Wellington street 
are, in many respects, makeshift, and the powdered fuel 
is conveyed by hand to a hopper, E, figure 2. In the 
base of this hopper is a small delivery wheel, 0, in the 
rim of which are notches c c. These notches are pro- 
vided with slides worked by a very simple arrangement, 
which compels them to obey the action of gravity and 
fall to the bottom of the notches when they are at the 
top of the wheel C. The notches then fill with coal- 
dust, and, as the wheel revolves, the slides, being thrust 
downward, push the coal out of the notches into the 
air tunnel B B. The rate of delivery of the coal can 



APPARATUS. 241: 



thus be accurately fixed by regulating the speed of the 
wheel C, which is driven by a face friction wheel, in a< 
way that will be readily understood. By setting the* 
friction wheel nearer or further from the axis of C\ the* 
speed of the latter can be altered without affecting that 
of any other portion of the apparatus. In order to mix. 
the coal-dust with the air, a twisted plate of metal, g g, 
is put in the air tunnel. This causes a rotary motion ins 
the current, and produces the required effect. B B is. 
prolonged into the firing place, and coupled on to the 
pipe B, figure one, by a socket. The air is supplied by 
a blower A A, figure two, driven by a belt from a lay- 
shaft. The apparatus is started by lighting a fire in the 
retort A, figure one. After this has burned up, if steam 
be available, the blower is set in motion and coal-dust* 
and air fed into the retort, the front of which is bricked 
up, as shown in the end view of the boiler, figure three. 
" Several experiments have been carried out to test 
the value of the apparatus. One by Mr. T. B. Jordan, 
of Queen Victoria street, lasted five hours and fifty-five 
minutes. The boiler evaporated 5984 pounds of water 
from eighty-one degrees with 720 pounds of coal, or 
8.312 pounds per pound of coal. In a previous experi- 
ment, lasting five hours, the same boiler, fired in 
the ordinary way, evaporated 10.194 pounds of water 
with 1568 pounds of coal, or at the rate of 6.501 
pounds per pound of coal. In a third experiment, 
made by Mr. Gr. Barker, of Birmingham, the trial 
lasting five hours and fifty-five minutes, 720 pounds 
(17) 



242 COMBUSTION OF COAL. 

of coal were burned, and evaporated 5984 pounds of 
water, or at the rate of 8.312 pounds per pound of 
coal from fuel at eighty-one degrees, the pressure being 
forty-two and one-half pounds. In an experiment with 
the same boiler, hand fired, the evaporation was 6.5 
pounds per pound of coal. 

" More recently we carried out ourselves an experi- 
ment which lasted two hours. The boiler was filled up 
to begin with, and the experiment commenced when 
the pressure was 44 pounds. During the run no water 
was fed into the boiler. After it was over the donkey 
was started and the boiler pumped up to the same level 
as at starting. The stop-valve being closed, the press- 
ure rose, notwithstanding the feed — a result due to the 
intense heat of the clay retort and fire-bricks. The 
whole quantity evaporated was thirty-five cubic feet, or 
twenty-one hundred and eighty-four pounds. The 
weight of coal burned was 176.5 pounds, and it follows 
that 12.3 pounds of water per pound of coal were evap- 
orated from and at a temperature of two hundred and 
ninety-one degrees. It will be seen that the rate of 
evaporation was extremely low for so large a boiler, and 
it is proper to add that the blower, which ran at an 
average speed of two hundred and sixty revolutions per 
minute, was driven by a lay-shaft running too slowly, 
but over which Mr. Stevenson had no control. The 
speed also varied considerably, which was against the 
performance of the apparatus. Throughout everything 
worked perfectly without a hitch or difficulty of any 



Plate TV. 




STEVENSON'S APPARATUS FOR BURNING POWDERED FUEL. 



stevenson's apparatus. 243 

kind; and the closing of the boiler front rendered the 
firing place exceedingly cool — a manifest advantage. 

A curious feature of Mr. Stevenson's apparatus is, 
that the quantity of air admitted per pound of coal 
admits of accurate determination. During the trial, at 
which we were present, the blower supplied 1.2 cubic 
feet of air per revolution. This was determined by 
measuring the capacity of the blower, and checking the 
result with a delicate anemometer, placed at the mouth 
of the coal delivery pipe, the coal being shut off. Now 
1.2 X 260 =312 cubic feet, or twenty-four pounds of 
air per minute. The coal supplied in the same time 
was two pounds nearly. Thus only twelve pounds, or 
the least possible quantity of air which will suffice for 
combustion, were supplied. Yet there can be no doubt 
that no smoke was produced, nor does it appear possi- 
ble that any coal-dust was deposited unconsumed in the 
flues. 

We have endeavored to place our readers in posses- 
sion of all the available information concerning a new 
and important branch of physical inquiry. It can be 
easily shown that in theory, at all events, the combus- 
tion of fuels in the form of dust ought to be attended 
with excellent results; and Mr. Stevenson proved that 
an apparatus can be made which will work without 
giving any trouble, and which is inexpensive and sim- 
ple. But we have, on the other hand, no data concern- 
ing the cost of breaking the fuel, and the apparatus is 
quite too small, or at least is run too slowly, to enable 
any estimate of its value to be formed which can be 



244 COMBUSTION OF COAL. 

based on fact and not on conjecture. The retort used 
by Mr. Stevenson is far too small, and consequently 
does not fit the flue properly. 

The retort must reduce the efficiency of the heating 
surface to some extent, as it is certainly not as hot as a 
furnace would be. 

It appears to be proved by the facts which we have 
placed before our readers, that a retort, or its equiva- 
lent, can not be dispensed with, and it is shown that a 
chemical equivalent of air will suffice to produce com- 
bustion without smoke. This last is an important fact, 
and would, standing alone, entitle the invention of Mr. 
Stevenson to consideration. 



CHAPTER XV. 

LIQUID FUEL. 

Analysis of Crude Petroleum— Quantity of Air Eequired to Burn 
Oil — Units of Heat Evolved by the Combustion of Oil — Evap- 
orative Power of Crude Oil — What is Claimed for Petroleum as 
a Fuel — Wise, Field and Aydon's System of Burning Liquid 
Fuel — Extraordinary Results Obtained — Advantages Arising 
from its Use on board Steamships and Vessels of War. 

Petroleum is a natural hydrocarbon oil. That of 
Pennsylvania, from whence most of the American petro- 
leum is shipped, is of a dark brown color, having a 
greenish tinge. In specific gravity it averages about, 
0.8, though it varies some .025 on either side of this 
figure. x\.s there is apparently no end to hydrocarbon 
combinations, the analysis of crude petroleum, as deter- 
mined by Professor H. Wurtz, will be given as best 
suited to our present purpose, which is as follows : 

Carbon 84 

Hydrogen 14 

Oxygen , 2 

100 

Deducting the oxygen and the quantity of hydrogen 
to form water, we have 



9 



.25 = useless hydrogen. 



246 COMBUSTION OF COAL. 

Then, 

14 — .25 = 13.75 available hydrogen, 

and 

2 + .25 = 2.25 water, 

or 

Carbon 84 

Hydrogen 13.75 

Water '. 2.25 

100 

The net theoretical quantity of air required to burn 
the carbon to carbonic acid, and the hydrogen to water, 
in the above composition, would be, 

.84 X 12 = 10.08 pounds of air for the carbon. 
.1375 X 95= 4.36 pounds of air for the hydrogen. 

The total estimated quantity of heat that can be 
given off, by the complete combustion of the above, 
would be, 

Carbon 84 X 14,544 = ]2,217 

Hydrogen 1375 X 62,032= 8,529 

20,746 units of heat. 

The theoretical evaporative power, or the number of 
pounds of water which may be evaporated at 212°, and 
at atmospheric pressure, by one pound of oil, as above, 
and containing twenty thousand seven hundred and 
forty-six heat units, the feed water being supplied the 
boiler at 80° Fahr., may be determined as follows : 

212° — 80° = 132° difference in temperature. 
966 4- 132 = 1098 



LIQUID FUEL. 247 



Then, 



1 ' ' — 18.89 pounds of water. 



The total equivalent evaporative power of one 
pound of oil, as above, from and at a temperature of 
212° Fahrenheit, and at atmospheric pressure is, 

-ggg- 21.47 pounds of water. 

In these several calculations the whole of the car- 
bon, and the excess of hydrogen only, have been used. 
The whole of the oxygen and the combining weight of 
hydrogen to form water have been deducted from the 
total analysis. It is probable that the figures given 
above represent a fair average of the total heating 
power of crude oil. The writer is not aware that any 
calorimeter tests of crude American petroleum have 
been made. 

It is claimed for petroleum that, on account of its 
superior heating power, a sensible reduction in the size 
of steam boilers may be made under that required for 
coal, or, the boiler remaining the same, more water may 
be evaporated, and thus its capacity increased. So little 
is known, however, of the actual economic efficiency of 
liquid fuel over coal, under all conditions, that the best 
form of furnace, and best design for the boiler, can 
hardly be said to have been practically determined. 

It certainly has cleanliness in its favor, as there are 
no ashes or clinkers left in the furnace. It also permits 
of continuous firing in a closed furnace, free from drafts 
of cold air. The quantity of heat required to maintain a 



248 



COMBUSTION OF COAL. 



constant pressure of steam may be controlled by the 
simple adjustment of a valve in the oil supply pipe. It 
is obvious that by this method of firing, one man may 
attend a number of furnaces, and thus dispense with 
firemen, coal heavers, and other attendants. 




bub. 




Figure 9. 



Several years ago (1868) Messrs. Wise, Field and 
Aydon's system of burning liquid fuel was illustrated 
and described in the "Engineering." The evaporation 
reported as having been obtained in actual practice is so 
near the theoretical calorific power of the fuel, that it 
seems almost impossible to improve upon a process 
yielding such high results. The engravings, figures 9 
and 10, show its application to a Cornish boiler; these 



LIQUID FUEL. 



249 



engravings, together with the descriptive matter accom- 
panying them, are reproduced from the above journal: 
"As will be seen from the engravings, the apparatus 
is a very simple character. It consists, in fact, merely 
of a super-heater arranged as shown, and a kind of 




Figure 10. 



injector placed in an inclined position just above the 
lire-door. The petroleum, or other liquid hydrocarbon, 
to be burnt, is led to the injector through a pipe fur- 
nished with a cock, by which the supply can be regu- 
lated, and it is there met by the steam which has passed 
through the super-heater, and which has thus had its 
temperature raised to about six hundred degrees. The 



250 COMBUSTION OF COAL. 

injector is very similar in its construction to Gi "fiord's 
well-known instrument, and its action is such that the 
liquid fuel is injected into the furnace in the form of an 
exceedingly fine spray mixed with the super-heated 
steam. In the case of the arrangement shown in figure 
9 the spray thus injected comes in contact with the 
hot ashes on the fire-bars, and is thus ignited; a com- 
bustion ensues which is very perfect, and which is under 
most complete control, the amount of flame being read- 
ily increased or diminished by regulating the quantities 
of liquid fuel and steam admitted to the injector. The 
air necessary to support combustion is admitted through 
openings in the fire-door, and so long as the apparatus 
receives the most ordinary amount of attention, the 
flame produced is perfectly smokeless. 

"As the liquid fuel is injected by the aid of super- 
heated steam, it is evident that a supply of steam must 
be obtained before the apparatus can be brought into 
action. This being the case, the arrangement shown by 
figure 9 will in many instances be that which it will 
be most convenient to adopt. In this arrangement the 
fire-bars are retained, and steam can thus be got up by 
an ordinary fire in the usual way. So soon as a certain 
pressure of steam has been obtained, the ordinary fire 
can be allowed to die out and the injector brought into 
action, the ashes remaining from the ordinary fire serv- 
ing to close the openings between the grate-bars and to 
ignite the spray of liquid fuel, as we have already 
explained. This arrangement is also convenient in cases 
where the boiler is worked sometimes with liquid fuel 



LIQUID FUEL. 251 



and sometimes with coal. In this case, the steam for 
injecting the liquid fuel may be obtained at starting 
from a small auxiliary boiler heated by an ordinary fire, 
it being, of course, merely necessary to use this auxiliary 
boiler until steam has been raised in the main ones. 

" Altogether the apparatus here described is the 
most simple and efficient that we have yet seen for 
burning liquid hydrocarbons. We have been informed, 
on what we consider reliable authority, that at Mr. 
W. C. Barnes' chemical factory at Hackney Wick, 
where his apparatus has been for some time at work, 
15,240 pounds of water have been evaporated in five 
hours by one of the boilers, by the consumption of 
eight hundred pounds of oil; or an evaporation of nine- 
teen pounds of water per pound of oil. Taking into 
consideration that the pressure at which the boiler is 
worked is twenty-eight pounds, and that the tempera- 
ture of the feed- water was 66°, this performance is 
equivalent to the evaporation at atmospheric pressure, 
from a temperature of 212°, of twenty-two pounds of 
water per pound of oil burnt. The fuel used is the 
waste product left from coal tar after the removal by 
distillation of the naphtha and light oils. It weighs 
about sixty-five pounds per cubic foot, and is a refuse 
material produced at the above factory. The apparatus 
is supplied with oil from a tank, which is in its turn fed 
from the upper part of another tank placed at a slightly 
higher level. This latter tank has a funnel-shaped bot- 
tom which receives the dirt or other heavy impurities 
deposited by the oil, a pipe being fitted to the lowest point 



252 COMBUSTION OF COAL. 

of the bottom, so that these impurities can be drawn 
off when necessary. The oil tank is also fitted with a 
coiled pipe through which steam can be blown in cold 
weather, or at other times if it should be necessary, to 
liquefy the oil. "We have ourselves seen the apparatus 
in action at Mr. W. C. Barnes' factory, and can testify 
to the perfect combustion obtained by its use. It has 
also, we may mention, been applied, amongst other 
places, to the boiler of a steam launch now at Woolwich 
dockyard, and we understand that it has in this case 
proved equally successful. 

" The question of to what extent liquid fuel can be 
economically substituted for coal, is one to which it is 
at the present moment very difficult to give even a 
general reply, whilst to give a precise answer is, of 
course, impossible. The question is, in fact, one upon 
which most persons proposing to use liquid fuel would 
have to decide for themselves. In every case the answer 
will depend greatly upon the comparative prices at 
which coal and liquid fuel can be obtained, and upon 
the certainty with which a supply of the latter fuel is 
procurable. In many instances the rate of evaporation, 
which we have above mentioned as having been obtained 
at Mr. W. C. Barnes' works, would be amply sufficient 
to justify the substitution of liquid fuel for coal, particu- 
larly where the fue\ is obtainable in sufficient quantities 
close at hand as a waste product ; whilst in other cases, 
where coal can be got at a very cheap rate, this latter 
fuel will have the advantage. Perhaps the nearest 
approach to a general answer which can be given to the 



LIQUID FUEL. 253 



question is, that so long as the cost of a certain quantity 
of liquid fuel does not exceed, or only very slightly 
exceeds, the cost of the amount of coal or other solid fuel 
necessary for doing the same work, there is an advan- 
tage in using the liquid fuel, there being a saving 
effected in the wear and tear of fire-bars, etc., and the 
cost of labor for firing being very greatly reduced. 

" So far we have only been speaking of land boilers. 
In the case of steamships, and particularly of war ves- 
sels, or steam yachts, the power of carrying fuel for an 
increased number of days' consumption is one which, 
in many instances, will outweigh all questions of cost. 
In hot climates, also, the adoption of liquid fuel would 
materially add to the comfort of the stokers, as in cases 
where it was used it would be comparatively easy to 
maintain the stokehole at a moderate temperature. 
Another point, which is of importance in the case of 
both land and marine boilers is, that it appears certain, 
from the experiments which have already been made, 
that a greater duty can be got out of any given boiler 
when it is worked with liquid, than when it is worked 
with solid fuel ; or, in other words, that with a given 
boiler a much greater quantity of water can be evapor- 
ated in a given time with the former fuel than with the 
latter." 



CHAPTER XVI. 

GASEOUS FUEL. 

Loss Attending the Use of Solid Fuels — Advantages Connected 
with the Use of a Gas -Fuel — Coal -Gas for Domestic Use — 
Water -Gas — Volume of Water -Gas Obtained for One Ton 
of Coal Burned — Strong's Process for Generating Fuel- 
Gas — Professor Gruner Quoted on the Great Waste of 
Heat in Several Metallurgical Processes — Comparison between 
the Efficiency of Crude -Coal and Water -Gas — Calorific Inten- 
sity of Water -Gas — Analysis of Water -Gas — Calorific Equiva- 
lent of Water -Gas — Flame Temperature — Economic Value of 
Water -Gas — Influence of the Specific Heat of the Products of 
Combustion of Water- Gas — Water -Gas as an Illuminating 
Agent — Objections to Water -Gas. 

There is always a loss attending the generation of 
heat from solid carbonaceous fuels, and perhaps quite 
as much more heat is lost in its application to any 
economic use. The loss is greater in proportion as the 
amount of coal burnt becomes less in quantity. Per- 
haps there is no single application of heat in which the 
loss is greater than that applied to the melting of met- 
als in crucibles. In this metallurgical operation the 
fire is often large, and urged to its utmost intensity, 
until the metal has reached the proper degree of fusion, 
when the crucible is removed and the fire abandoned. 
This will apply in almost any case where an intense 
heat is required, and its use confined to certain fixed or 
arbitrary working hours. In this respect liquid or gas- 
eous fuels have an advantage over solid fuels, as they 
need not be lighted until the last moment, the nature of 



GASEOUS FUEL. 255 



the fuel permitting a concentration of heat at any 
desired point of application, and in any degree of inten- 
sity; it is also, at all times, under perfect control, and 
the supply may be instantly cut oft' when no. longer 
required. 

"Another cause of loss in the burning of crude fuels, 
and one of sufficient importance to deserve mention, is 
the fact that there is mixed with the carbon a con- 
siderable quantity of foreign matter not combustible, 
which absorbs heat and gives no equivalent. This is 
represented principally by the ash and clinker, which 
every consumer of coal knows to be a large item. It 
reaches from ten to fifteen per cent, of the material 
paid for. To illustrate the difficulties attending the use 
of a crude form of fuel, let us take the most familiar 
methods, such as are employed in domestic cooking and 
heating (6J). 

"Ignoring the mechanical imperfections of stoves 
and furnaces, lest an examination into them should 
extend this article unduly, we will examine the more 
evident sources of loss : 

" a. The expenditure of fuel in generating heat at 
times when it is not utilized. Every housekeeper must 
have been struck with the fact that a large amount of 
wood and coal is burned before the range is ready to 
cook, and that a probably larger amount still is used 
after the cooking is done. Annoying as this may be, it 
is cheaper to keep the lire up between meals, even in 
summer-time, when it is undesirable, than to let it go 
down and re-kindle three times. 



256 COMBUSTION OF COAL. 

u b. The excessive quantity employed while in use. 
Often to accomplish some trifling result, like the boiling 
of a tea-kettle, the whole area of fire space is necessa- 
rily kindled, though not more than one-tenth of it is 
required. Twenty pounds of good anthracite coal con- 
tain heat-energy sufficient to raise two hundred and 
seventy thousand pounds of water one degree in tem- 
perature, or seventeen hundred and seventy-six pounds 
from sixty degrees Fahrenheit to the boiling point, two 
hundred and twelve degrees Fahrenheit, and yet it is to 
be feared this power is frequently employed in cooking 
a pot of coffee. If we have expended for our morning 
draught heat enough, if perfectly applied, to raise three- 
fourths ton of the same liquid from atmospheric tem- 
perature to boiling point, it may be considered a some- 
what luxurious beverage. 

" c. The items of labor and inconvenience incident 
to the use of coal are too apparent to need any enlarge- 
ment. 

" These are the principal arguments against the 
general use of fuel in its natural condition, and thev 
appear formidable enough to justify the assertion that 
not over ten per cent, of the heating power of such fuel 
is utilized. 

"Let it be remembered that it is in all cases gas only 
that we burn, and from which we derive heat, so that 
the question is really whether each family can make a 
limited quantity of the gas as economically and success- 
fully in very defective ranges and stoves, as the same or 
a much better article can be manufactured on a large 



GASEOUS FUEL. 257' 



scale at some great establishment whence it could be: 
distributed to consumers. There can be no doubt that 
the advantage possessed by all concentrated industries- 
exists in this one to at least as great a degree as in any. 
other department of manufacture. We might as rea- 
sonably expect to grind our own flour, or weave our 
own fabrics economically, as to successfully compete 
with large gas-works properly constructed and skillfully- 
managed. 

" The advantages connected with the use of a gas-fuel 
may be enumerated as follows : 

" a. The cost, labor and inconvenience of handling 
a heavy material is avoided, the fuel being capable of; 
easy distribution. 

u b. It is in a form also free from those material 
impurities which involve a large residual waste, besides 
impairing combustion. 

" c. It is free also (if it be a purely combustible gas) 
from those ingredients which, in the present methods of 
heating, involve even larger loss than the cause last 
mentioned. 

" d. It is in precisely the condition to unite perfectly 
and instantaneously with the oxygen of the air, thus 
securing a thorough combustion. 

u e. Hence it gives an immediate and uniform result, 
and its flame temperature is constant. 

"/. The intense and steady heat of the flame just 
mentioned saves both time and money, by presenting 
an even fire-surface ready at the moment of ignition. 
(18) 



258 COMBUSTION OF COAL. 

u g. It is a fire capable of concentration upon the 
precise point where the result is desired, and one that is 
thoroughly under control, the turning of a valve start- 
ing, graduating, or stopping the combustion at will. 

u 'h. The general cleanliness of the system, no dirt 
or residuals being left. 

" i. The decided advantage from a sanitary stand- 
point of simply burning combustible gases in our dwell- 
ings, instead of attempting to make them as well,. by 
means of the imperfect gas machines called stoves. In 
the one case the only risk arises from the possibility of 
a leak, readily detected by the senses, and having simple 
mechanical remedies; in the other it is a much more 
serious risk, because the defect is a chemical one, conse- 
quent upon imperfect combustion, and the infusion of 
poison into the atmosphere is likely to be frequent and 
insidious, to say nothing of the deoxidation of the air 
by contact with red-hot iron surfaces. The reduction of 
this particular danger is about in proportion of the 
greater completeness of the combustion of the more 
refined fuel. 

"These facts appear to be overwhelming arguments 
in favor of a gaseous, as against a gross form of fuel, 
and lead to the inquiry, what gases are available for 
such purposes? 

" The ordinary coal-gas made for illuminating pur- 
poses possesses some of the requisite qualities. It is a 
combustible gas of great purity, of sufficiently low 
density to render its distribution easy, and with a high 
flame temperature; but, per contra, the constituents 



GASEOUS FUEL. 259 



which impart the illuminating power are expensive, 
while entirely unnecessary for fuel purposes. And yet, 
high-priced as it is, practical experience in its use 
proves that, in some departments at least, it is certainly 
cheaper than coal, besides its collateral advantages; 
and it is at the present time employed, to a limited 
extent, by those who have become familiar with the 
facts. Exceedingly interesting tests have been made 
by the London engineers with city gas, developing 
some economic features in the matter quite surprising; 
and at the meeting of the American Gas-Light Asso- 
ciation, in 1877, a paper was presented by one of the 
members showing that careful experiments had so thor- 
oughly demonstrated its saving, even at three dollars 
per one thousand cubic feet, that nine-tenths of his cus- 
tomers were using it in preference to wood or coal for 
kitchen and laundry purposes. 

"Nevertheless, coal-gas can hardly be expected to 
offer, for general use — domestic and industrial — a sub- 
stitute cheap enough to supplant coal. Something at a 
still lower price is needed. Such gas as is made by the 
Siemens process, before alluded to, has the advantage of 
cheapness, so far as the mere relation of cost and quan- 
tity is concerned, as it can be produced at about fifteen 
cents per one thousand feet, but its composition is not 
favorable. It in fact contains less than thirty per cent, 
of combustible gases, the remainder being worse than 
useless, besides rendering it too heavy for ready distri- 
bution at long distances. 



260 COMBUSTION OF COAL. 



WATER GAS. 

a A water-gas — that is, a gas resulting from the 
decomposition of steam by contact with incandescent 
carbon — if it can be made cheaply, possesses those very 
qualities most desirable in a fuel, viz, inflammability 
and intensity. 

" Composed of hydrogen and carbonic oxide, it is 
free from the undesirable element, nitrogen; and what 
an advantage lies in that single fact, it is hoped the fore- 
going explanation may have made measurably apparent. 
If carbonic oxide representing the maximum flame 
intensity (among practical gases), and hydrogen with 
but little less of this quality, and an even 'greater use- 
ful value,' as Percy expresses it, do not furnish the very 
highest order of fuel, then science does not yet know 
where to seek it. Fortunately, too, it is a fuel obtaina- 
ble at the lowest cost, though this is a recent achieve- 
ment. For more than half a century inventors of dif- 
ferent nationalities have racked their brains for some 
method by which water-gas could be produced in large 
quantities inexpensively for the industrial arts, but 
various defects have invariably attached to the systems 
proposed and rendered them unsuccessful. 

"It requires the outlay of great potential energy to 
release the hydrogen of water, but the Lowe apparatus, 
by a system at once original and simple, generates a 
concentrated and sustained heat which does the work 
with a facility that is astonishing, yielding a volume of 
fifty thousand feet for a ton of coal burned. 



strong's process for generating fuel gas. 261 



M. H. STRONG'S PROCESS FOR GENERATING FUEL GAS. 

"Adopting the economic principle of interior com- 
bustion throughout, viz, burning the coal in a primary 
chamber, or generator, and the products of its partial 
combustion in a secondary one, wherein the heat is 
stored for subsequent utilization, there are novel features 
in the Strong process, which give it very definite advan- 
tages in the rapid and economic generation of a com- 
bustible gas of remarkable purity and efficiency for fuel 
purposes. 

" Reference to the accompanying diagram, plate V, 
will make intelligible the following description of the 
apparatus and its operation : 

" The generator is charged with lump coal or coke, 
entered at the door in its side, or from above through 
the opening left by the removal of the hopper Z, which 
is removable by means of a lever and tramway. An 
air-blast enters below the hydraulic grate-bars at W, 
which drives the fire and forces over into the adjoining 
chambers, laid up with loose fire-brick like a Whitwell 
stove, the products of partial combustion (Siemens gas), 
which are ignited therein by a second blast entering 
through a perforated tiling at X, and burn downward 
among the brick work, following the direction of the 
arrows. The third chamber, filled, like the second, with 
refractory material, absorbs a part, at least, of the heat 
of the waste products, which escape at the top through 
an open valve, shown in the diagram as closed. 



262 COMBUSTION OF COAL. 

"When the coal has attained a heat of say red to 
bright red, the brick of the super-heater (as the second- 
ary chambers are termed) show orange to white. 

"The air-blasts are then shut off, the valve before 
mentioned is closed as in the cut, and steam is admitted 
just below it at Y. Passing in the reverse direction of 
the arrows, it becomes intensely heated by contact with 
the bricks, from which it emerges into the top of the 
generator, where it meets at V, a shower of coal-dust 
sifted downward from the hopper Z, hj means of an 
Archimedean screw slowly revolved. 

" The steam has acquired such an increment of heat 
that, by contact with the dust-carbon, a mutual decom- 
position instantly ensues, and the gases resulting pass 
downward through the bed of coal and out below the 
grate-bars into a hydraulic main. 

"Astonishing as this original method of decomposi- 
tion may appear, there is no doubt of its occurrence at 
the point V, as during the earlier experiments the gases 
were allowed to escape from the generator without 
passing through the incandescent coal. There was 
found, however, an excess of carbonic acid in the pro- 
duct, and some unconverted particles of carbon were 
carried over. Both these defects were remedied by the 
passage of the gases through the burning coal, the car- 
bonic acid changing to the oxide of carbon and the 
unburnt dust being arrested and utilized as fuel. The 
theory that the rapidity in evolution of the gas is pro- 
portioned to the reduced size of the carbon particles is 
fully confirmed by test made upon pulverized peat, dur- 



F 







M. H. STRONG'S APPARATUS FOB GENERATING FUEL GAS. 



strong's process for generating fuel gas. 263 

ing which the volume of gas for a given period was 
increased about fifty per cent, as compared with the 
coal slack. 

"The operations of the apparatus at Mount Vernon, 
in New York, where experimental practice has extended 
through the past year, substantiate the claim that a pure 
water-gas can be obtained at the expenditure of not 
over 2,240 pounds of coal for each 50,000 cubic feet. 
This includes the quantity burned under the boiler, 
which amounts to from twenty-five to thirty per cent, of 
the whole. But it would seem that this considerable 
amount expended in the generation of the steam, may 
be saved by a simple utilization of the heat of the alter- 
nating waste and gaseous products which, under those 
experiments, escaped at from 800° to 1,200° Fahr. 

"It is confidently believed that if these hot gases 
we're employed to heat the air-blast and the water, the 
product of combustible gas would be increased to from 
65,000 to 70,000 cubic feet for each ton of coal. 

"The most striking advantages of the Strong pro- 
cess are, 

"1. The extreme rapidity with which the gases are 
generated in lar^e volumes. 

"2. The variety of materials which may be em- 
ployed, and their low cost. 

" 3. The remarkable purity of the product. 

"4. The economy of the labor involved. 

"Regarding the first claim, it maybe stated that a 
furnace of the dimensions shown in the diagram will 
deliver fullv ten thousand cubic feet for each run of 



264 COMBUSTION OF COAL. 

thirty minutes. The alternate thirty minutes is used for 
re-heating, as in the Lowe process. A pair of such 
furnaces to secure continuity of operation, could be 
relied on to furnish nearly five hundred thousand cubic 
feet per day, and the labor requisite to run them would 
be but two men for each twelve hours. 

" ^Tot only can anthracite or bituminous coals be 
used but lignites and coke are available, and, what is 
very important, their culm or slack can be employed in 
the proportion of three-fourths, with very positive 
advantages. In fact, the ability of this system to utilize 
dust-carbon has been tested even to the successful use of 
peat, as already mentioned. 

"It will be seen, therefore, that this method does 
not depend upon any special forms of material, but, on 
the contrary, employs many, some of which are abund- 
ant and inexpensive. In consequence of this and the 
advantage first mentioned, the gas can be produced at 
the lowest possible price. 

"The extraordinary purity of the gas derived by 
this system is another exceedingly important fact. 
Analysis by Dr. Gideon E. Moore prove that the 
unpurihed gas contains only 12.90 grains of sulphur, 
which is considerably less than the legal limitation for 
the purified gas furnished to London. But the absence 
of any large percentage of non-combustible constituents 
is far more important, as will be observed by the fol- 
lowing table : 



265 



Oxygen 0.77 

Carbonic acid 2.05 

Nitrogen 4.43 

Light carbonic hydrogen 4.11 

Carbonic oxide 35.88 

Hydrogen 52.76 

"The relatively small proportion of N" and C0 2 will 
undoubtedly be reduced yet lower by an apparatus on a 
larger scale than the one in use at Mount Vernon, as 
the residual air left in the stack at the time of shifting 
from the blast to gas -making would be proportionately 
smaller, and this is the principal source of these non- 
combustibles. 

"It will be apparent that this composition repre- 
sents the best mixture for calorific purposes known to 
science. It is in striking contrast to that produced by 
the Siemens furnace, which, at about the same cost, 
contains about two-thirds of non-combustibles. This 
serious drawback has been a characteristic of all other 
cheap gases heretofore, and is a fatal objection in any 
method aiming to supply the general demands of a fuel 
gas. Aside from the fact that such a heavy dilution 
impairs the efficiency and value of a gas to an extent 
not generally understood, the addition of such a useless 
volume would necessitate an excessive size and cost of 
mains for its distribution. 

"It becomes necessary here to explain a popular mis- 
conception which has led many intelligent minds to an 
entirely false conclusion regarding the economic advan- 
tages of gaseous forms of fuel as compared with crude 



266 COMBUSTION OF COAL. 

ones. It grows out of the axiom that in the conversion 
of the steam and carbon into their resulting gases there 
is an inevitable expenditure of thermal force, so that 
the new form of fuel represents less theoretic units of 
heat than the old, and that, in consequence, there is a 
loss rather than a gain by the exchange. 

"This is undeniable, but it is surprising that it 
should be so often misapplied in practical calculations, 
because the comparison lies between the two forms of fuel, 
not upon their mere theoretic calorific values, but upon the 
useful effects obtainable from each in practice. 

" The plain business question which presents itself, 
therefore is, what advantage does the Strong gas possess 
over the coal from which it was produced in actual 
operations ? Let us investigate this carefully. 

"The standard principle for obtaining the calorific 
or heating power of any fuel is to ascertain how many 
weights of water one weight of it will raise one degree 
of temperature, if burned under the best possible con- 
ditions in air — and the number of weights so deter- 
mined are called the heat-units of that fuel. These of 
course symbolize its maximum calorific power. Thus, 
dried peat is said to possess nine thousand nine hundred 
and fifty-one units of heat; asphalt, sixteen thousand 
six hundred and fifty-five; good anthracite, thirteen 
thousand per pound. That is, the total heat of the 
perfect combustion of one pound of anthracite would 
raise thirteen thousand pounds of water one degree 
Fahrenheit. But in estimating the practical heating- 
power of these and other substances we must remember 



strong's process for generating fuel gas. 267 

that it is not possible to obtain a result even remotely 
approaching these figures, because instead of burning 
them upon nicely adjusted laboratory principles, our 
ordinary methods of combustion are grossly imperfect 
and extremely wasteful. An explanation of the why 
and wherefore of this would be interesting did the 
limits of this article permit, but a statement of the fact 
with some authoritative comments thereon must suffice. 
Professor Gruner, in a paper of which the following 
abstract was published in the Engineering and Mining 
Journal, volume twenty-one, number eight, states that: 
" ' In the wind-furnace, which is, from this point of 
view, the most imperfect apparatus, there is utilized, in 
the fusion of steel in crucibles, but 1.7 of the total heat 
capacity of the fuel, or at most three per cent, of the 
heat generated. In the reverberatory, when steel is 
melted in crucibles, the useful effect is two per cent, of 
the total heat, or three per cent, of the heat generated. 
In the Siemens crucible furnaces, 3 to 3.5 per cent.; in 
Siemens glass furnaces, operating on a large scale, 5.50 
to 6 per cent.; in ordinary glass furnaces, three per cent.; 
in fusion upon the open hearth of a reverberatory, of 
glass, seven per cent.; of iron, eight per cent. 

."'In well-arranged Siemens and Ponsard furnaces, 
up to fifteen, eighteen and even twenty per cent, of the 
total heat is utilized. The calorific effect is much 
greater when the fuel is mixed with the material to be 
fused. Large iron blast furnaces utilize according to 
their working, seventy to eighty per cent, of the heat 
generated, or thirty-four to thirty-six per cent, of the 



268 COMBUSTION OF COAL. 

total heat which the complete combustion of the fuel 
would set free.' 

"We are thus furnished a basis of comparison 
between the efficiency in actual practice of crude coal 
and water-gas, for it is estimated that by reason of its 
instant mixture with the oxygen of the air, the combus- 
tion of the gas is so perfect that the heat generated 
would be ninety per cent, of the full theoretic power by 
any rational system which would use the available heat 
in the products of combustion. 

" Therefore, while 2,240 pounds of coal represent a 
total theoretic value of 29,120,000 heat-units, the value 
really utilized by the best modern blast furnace, accord- 
ing to Professor Gruner (thirty-six per cent.) w^ould be 
9,483,200. 

" The weight of gas which the same ton would pro- 
duce, viz, two thousand and fifty pounds, possesses a 
total value of 18,035,900 heat-units, of which 16,232,310 
are actually available in practice, showing an advantage 
of the new fuel against the old as 1.71 is to 1. This 
advantage, moreover, exists upon the basis of a similar 
price for the coal employed in the two cases, while in 
fact there is a still further gain in favor of the gas, 
owing to the fact that it makes available a much cheaper 
material (slack) than can be employed in the direct fur- 
nace operation — a difference at tide- water of about 
2.5 to 1. 

"The comparison becomes still more favorable to 
the gas fuel if applied to ordinary domestic uses. In 
that department, it is generally conceded that ten per 



strong's process for generating fuel gas. 269 

cent, of the theoretic heating power of coal is the best 
result obtained, so that in these uses the gas would have 
an advantage of about 5.57 to 1. 

" Let us now, for convenience, write down not the 
theoretic, but the practical, available heat-units side by 
side for comparison, as we have ascertained them 
above. 



ONE LB. COAL. STRONG GAS FROM 1 LB. COAL. 

= ^ LB. GAS. 
(THEORETIC UNITS 8.798 PER LB.) 



(THEORETIC UNITS 10.000.) = ru 



CRUCIBLE LARGE DOMESTIC 



FURNACES. BLAST DO. USE. IN EITHER USE. 

Per cent of heat util- 
ized 3% 3G . 10 90 

Units available in 

practice 453 4,6S0 1,300 7,246 

" This allows ten per cent, loss in the combustion of 
the gas, which is the probable extent of this waste. In 
some metallurgical operations a further allowance may 
be necessary to cover an imperfect utilization of the 
escaping- products, but as this loss is variable with 
different methods we leave the computations to the 
reader. 

"This, it is insisted, is the proper method of estimat- 
ing the actual relative thermal values of the two forms. 

"Beyond this first economic gain are collateral ones, 
affecting not only cost but other equally important 
questions of time (which is a synonym for money) and 
the quality of the products. Take, for example, the 
advantage of a fuel which can be turned on by a valve, 
lighted on the instant, and extinguished as quickly. 
Aside from the tedious time necessary to the firing up 
of a metal furnace, an element of expense, how largely 



270 COMBUSTION OF COAL. 

the labor incident to the care of such operations would 
be reduced. 

" Another feature worthy of special comment is the 
intensity of combustion of a gas fuel. The theoretic 
power of the Strong gas is 5483°* Fahr., and the relation 
of this fact to rapid and economic operation is too mani- 
fest to require argument. A furnace will often stand 
indefinitely at a temperature just short of that required 
to accomplish its work, at an incalculable loss of time, 
money and temper, and sometimes to the serious disad- 
vantage of the product. The writer has seen a small 
experimental reverberatory for the burning of this gas 
ready to charge in twelve minutes from lighting, and 
iron melted therein in eight minutes thereafter. 

" Again, the constancy of this gas flame is another 
very marked advantage, and will enable the mechanic, 
once the proper admixture of air is ascertained, to yield 
a heat adapted to his special wants, to maintain a uni- 
form temperature and obtain a uniform result in- time, 
cost and quality. 

"The whole subject is. one of peculiar interest and 
opens many avenues of inquiry and experiment." 

The following is a copy of a report by Dr. Gideon E. 
Moore on water gas as made by the apparatus and pro- 
cess just described. He visited the gas works at Mount 
Vernon, 23". Y., October, 1877, obtaining samples of the 
gas, which were analyzed by him, with results as given 
below. 

This report is an interesting contribution to the lit- 
erature of gaseous fuel, and though repeating much 



FUEL GAS. 271 



that has already been said and explained in the earlier 
chapters of this book, it is deemed best for the sake of 
clearness and comparison to print the report without 
alteration or erasure, which is as follows : 

" The gas was made on the day previous to my visit, and I was 
assured by Mr. Strong that no lime had been used, nor other puri- 
fying agent except the water in the hydraulic main. The gas was 
allowed to pass freely from the gasholder through a series of glass 
tubes for two hours, to displace the air, after which the tubes were 
hermetically sealed by melting the ends, and the gas preserved in 
this state until required for use. 

" The specific gravity of the gas was determined by direct weigh- 
ing. The analysis was made by the methods laid down in Bunsen's 
gasometry, the more important determinations being made in 
duplicate — the carbonic oxide, for instance, being determined 
both by eudiometric analysis and by absorption with cuprous 
chloride. 

" The specific gravity of the dry gas was found to be 0.5408, air 
being unity, whence one cubic, foot weighs 0.04116 pound. The 
composition by volume was found to be as follows, viz : 

Oxygen 0.77 

Carbonic acid 2.05 

Nitrogen 4.43 

Carbonic oxide 155.88 

Hydrogen 52.76 

Marsh gas 4.11 

100.0U 

" Had the carbonic acid been completely reduced to carbonic 
oxide, thegas : after deducting the 0.77 per cent, of oxygen and 2.91 
per cent, of the nitrogen as air, would have presented the following 
composition, viz : 

Nitrogen 1.55 

Carbonic oxide '. 40.C4 

Hydrogen 53.0:3 

Marsh gas 4.18 

100.00 

<: It is interesting to compare these figures with the theoretical 
result of the action of steam on anthracite coal. 

11 According to Percy, the combustible portion of Pennsylvania 
anthracite consists of 



272 COMBUSTION OF COAL. 



Carbon 94.63 

Hydrogen 2.73 

Oxygen 1.28 

Nitrogen 1.36 

100.00 

"If we assume that the 2.73 parts of hydrogen are evolved in 
combination with 8.19 parts of carbon in the form of marsh gas. 
100 parts of anthracite, free from ash. would require for the complete 
conversion of the residual, 86.44 parts of carbon to carbonic oxide 
115.25 — 1.28 = 113.97 parts, by weight, of oxygen or 128.22 parts of 
water. The gaseous products of the transformation of one hundred 
pounds of pure anthracite would, therefore, be, 

Nitrogen 1.36 

Carbonic oxide 201.69 

Hydrogen 14.25 

Marsh gas 10.92 

228.22 

or, reduced to per centages, 

BY WEIGHT. BY VOLUME. 

Nitrogen 0.60 0.32 

Carbonic oxide 88.38 47.89 

Hydrogen 6.24 47.25 

Marsh gas 4.78 4.54 

100.00 100.00 

" On comparing these figures with the analysis of Strong's gas, 
it will be seen that the proportion of marsh gas is virtually identi- 
cal in both cases, showing that it must have resulted solely from the 
destructive distillation of the coal, and not by direct synthesis. The 
gas formed by the action of superheated steam on charcoal possesses, 
according to Bunsen, the composition, 

Carbonic acid 14.65 

Carbonic oxide ...... 29.15 

Hydrogen 50 03 

Marsh gas 17 

100.00 

" it will be observed that the amount of carbonic oxide in 
Strong's gas falls somewhat short of the theoretical proportion, 
while there is a corresponding excess of hydrogen. This is attributa- 
ble partly to the absorption of oxygen in the oxidation of metallic 
sulphurets in the coal, partly to the formation of carbonic acid and 
its retention in the ash or removal by solution in water, perhaps 
partly also to the presence of oxidized products in the small pro- 
portion of tar. 



FUEL GAS. 273- 



"On the twenty-eighth of December 1 made a careful sulphur 
determination on gas made in my presence, and taken as it flowed, 
from the scrubbers to the gasholder ; no other purification having; 
been employed. The gas was found to contain 12.96 grains of sul- 
phur to the one hundred cubic feet — an amount surprisingly smal), 
at first sight, but less so when we consider that the two products ot~ 
the action of steam on highly heated sulphurets, viz, Sulphureted.! 
hydrogen and sulphurous acid immediately re-act on each other- 
with the formation of free sulphur and water. It is, therefore, evi- 
dent that the sulphureted hydrogen in the gas is simply the excess, 
over that which is decomposed by the sulphurous acid, and that this, 
must, at the most, be small in amount is equally evident from the- 
fact that anthracites are, as a rule, much freer from sulphur than 
bituminous coal, and that they are especially free from the organic 
sulphur compounds which, by destructive distillation, yield the vola. 
tile sulphur compounds so difficult of removal from ordinary coaL 
gas. The sulphureted hydrogen in the Strong gas is easily remov- 
able by the simplest means. 

CALORIFIC ELEMENTS OF THE STRONG GAS. 

" Calorific Equivalent — The theoretical calorific equivalent or heat- 
ing power of combustibles, is the amount of heat evolved by the 
combustion of the unit of weight thereof, expressed by the number 
of units of weight of water which can thereby be raised in tempera- 
ture one degree on the thermometric scale. 

" In England and America the unit of weight is the avoirdupois 
pound, the measure of temperature the Fahrenheit thermometer. 
One unit of heat, therefore, is the quantity of heat which will raise, 
the temperature of one pound of water one degree on the Fahren- 
heit scale, and n units of heat the amount which would be required 
to raise n pounds of water one degree Fahrenheit in temperature, 
or one pound of water n degrees. 

" In the case of a compound combustible, or, more properly, a 
mixture of several combustible substances, like the Strong gas, the 
theoretical calorific equivalent is obtained by multiplying the 
weights of the different ingredients, expressed as decimals of a 
pound, by their several caloritic equivalents as previously deter- 
mined by experiment. The sum of the numbers so obtained 
expresses the theoretical calorific equivalent of the mixture. 
In the following computations I have taken as a basis the fig- 

(19) 



274 COMBUSTION OF COAL. 



ures of Favre and Silberman, whose experimental researches are 
the most exact we possess. 

" Applying these principles to the analysis of the Strong gas, 
we have, 

COMPOSITION CALORIFIC 

IN DECIMALS EQU1VA- 

OF 1 POUND. LEN1S. 

Oxygen 0.01740 x 0.0 = 0.0 

Carbonic acid O.0G372 x 0.0 = 0.0 

Nitrogen 0.08798 x 0.0 = 0.0 

Carbonic oxide 0.70969 x 4325.4 = 3060.7 

Hydrogen 0.07473 x 62031.6 = 4635.1 

Marsh gas 0.04648 x 23513.4 = 1092.9 

1.00000 8797.7 

Hence the theoretical calorific equivalent of the* Strong gas is 
8,798 units of heat. 

FLAME TEMPERATURE. 

"By the flame temperature is understood the temperature pre- 
vailing in the interior of a burning mixture of gases. It may be 
computed from the calorific equivalents when the specific heat of 
the gaseous products of combustion is already known. The result 
is very different, according as the mixture burns under constant 
pressure, or with constant volume. The first case is the only one 
of which we have here to treat. 

"At 62° Fahrenheit one cubic foot of the Strong gas weighs 
0.04116 pound, and requires for its perfect combustion 2.47 cubic 
feet of air, weighing 0.1880 pound. Proceeding to the computa- 
tion of the calorific equivalent of one pound of the mixture of air 
and gas in these proportions, we have, 

COMPOSITION CALORIFIC 

IN DECIMALS EQU1VA- 

OF 1 LB. LENTS. 

Nitrogen 0.6557 x 0.0 = 0.0 

Carbonic acid 0.0105 x 0.0 = 0.0 

Oxygen 0.1964 x 0.0 = 0.0 

Carbonic oxide 0.1174 x 4325.4 = 507.6 

Hydrogen 0.0124 x 62031.6 = 706.5 

Marsh gas 0.0076 x 23513.4 == 176.9 

1.0000 1451.0 

whence the calorific equivalent of the mixture is 1451.0 units. 
The specific heat of the products of combustion results from the 
following considerations, viz: 



FUEL GAS. 275 



COMPOSITION 
IN DECIMALS SPKCIFIC 

OP 1 LB. HEAT. 

Nitrogen 0.6557 x 0.2440 = 0.15999 

Carbonic acid 0.2160 x 0.2164 = 0.04676 

Water vapor 0.1283 x 0.4750 = 0.06092 



1.0000 0.2G767 

whence the specific heat of the products of combustion is 0.20767. 
Dividing by this, the calorific equivalent previously found, we have 

1451.0 -f- 0.26767 = 5420.9° Fahr., 

the theoretical elevation of temperature by combustion above the 
initial temperature of the combustible mixture. If this initial 
temperature be sixty-two degrees Fahrenheit, the theoretical tem- 
perature of the flame will be 

5420.9 + 62 = 5482.9° Fahr. 

"This temperature lies beyond the point at which dissociation 
commences, and hence would never be attained in practice, as, 
however, Bunsen* has shown that the percentage of dissociation 
increases from the point at which it commences, through the 
higher temperatures, being for instance, in the case of a mixture 
in equivalent proportions of hydrogen or carbonic oxide and oxy- 
gen, fifty per cent, at 2,000°C. = 3,632°F. and 6Gf per cent, at 
3.000°C. = 5,432°F., we may safely assume that in the case of differ- 
ent gases the temperatures attained in practice will be, within cer- 
tain limits, proportional to their respective theoretical flame temper- 
atures. The experiments of Bunsen show that the extreme tem- 
perature which may be attained by the oxyhydrogen blast will not 
exceed 5,432° Fahr. According to H. Valerius f the theoretical 
flame temperature of ordinary illuminating gas in pure oxygen is 
13,509° Fahr., whereas in air it is 4,588° Fahr., or about 900° Fahr. 
below that of the Strong gas. 

"It is hardly necessary to add that dissociation of the products 
of combustion only affects the temperature of the flame, and has noth- 
ing to do with the quantity of heat evolved during the combustion. 

ECONOMIC VALUE OF THE STRONG GAS. 

" In the consideration of the economic value of the Strong gas 
the two applications which pre-eminently demand our attention, 
are, 

*PoggendorfFs Annalen, CXXXL, 171. 
tLes Applications de la Chaleur. 



!76 COMBUSTION OF COAL. 



" 1. Its value as a substitute for other forms of gaseous or solid 
fuel, in the arts and for domestic use. 

"2. Its application for illuminating purposes either, after 
previously charging it with illuminating substances, as a substi- 
tute for ordinary illuminating gas, or as a diluent for very rich 
coal gas. 

"Taking these subjects in the order I have indicated, I first 
pass to the consideration of 

" The Comparative Value of the Strong Gas as Fuel — As has already 
been shown, the Strong gas possesses a heating power of eight 
thousand seven hundred and ninety-eight units, and a flame tem- 
perature of 5,483° Fahr. One cubic foot of the gas, weighing at 62° 
Fahr., 0.0411 pound requires for its perfect combustion 2.47 cubic feet 
of air, and yields 3.027 cubic feet of products of combustion, of 
which 0.610 cubic feet is aqueous vapor, and 2.417 cubic feet perma- 
nent gases. 

"In the combustion of gaseous fuel, under normal conditions, 
and with perfect utilization of the heat of the fire gases, the only 
loss of heat is from radiation. Allowing ten per cent, as the prob- 
able extent of this waste, we have, for the effective heating power 
of the Strong gas — seven thousand nine hundred and eighteen 
units per pound, or one hundred pounds of pure anthracite, yield- 
ing, as has previously been shown, 228.22 pounds of gas, would 
develop in practice a heating effect equal to 228.22 X 7,917.91 = 
1,807,025 units of heat. The theoretical heating effect of coal being 
thirteen thousand units, the one hundred pounds of coal would, 
if directly burned, develop one million three hundred thousand 
units, of which, however, but about fifty per cent., or six hundred 
and fifty thousand units, would be realized under ordinary condi- 
tions in practice, hence the practical heating effect of the gas stands 
to that of the coal from which it was directly derived as 2.78 to one, 
whereby it is, of course, assumed that no loss of gas has been 
experienced during the manufacture. 

" In the manufacture, however, there is a large consumption of 
coal for heating the generator and for the production of steam. 
According to the inventor's figures, fifty pounds of coal will pro- 
duce one thousand cubic feet of gas, weighing 41.lt) pounds, and 
possessing the theoretical heating effect of three hundred and 
sixty-two thousand one hundred and thirteen units, of which three 
hundred and twenty-five thousand nine hundred and two units 
would be realized in practice. Fifty pounds of coal possesses the 



FUEL GAS. 277 



theoretical heating effect of six hundred and fifty thousand units, 
of which but three hundred and twenty-five thousand would be 
realized in practice under ordinary conditions and by continuous use, 
as in the generation of steam. Hence, in practice, and under equal 
conditions as to radiation and continuous nse, the gas will produce 
the full heating effect of the coal consumed in making it. 

"The cost of the gas being, according to Mr. Strong's estimate, 
from six to eight cents per one thousand cubic feet, and the cost 
of anthracite being but one dollar and a half per ton for 'pea and 
dust' coal, the cost of the coal required would be but 3£ cents, 
whence, assuming that there can be realized from such coal fully 
fifty per cent, of the theoretical heating effect, it follows that for 
such purposes as the generation of steam with blast air and contin- 
uous firing the Strong gas could not compete with such coal. 

"The case is, however, very different in the very numerous 
class of applications, in which the cheapest grades of coal can not 
be used. Thus, with ordinary steam and manufacturing coal, of 
which the price at New York is at present four dollars and a half 
per ton, the fifty pounds of coal would cost ten cents, which, con- 
trasted with the average cost of the Strong gas, seven cents, shows 
the great economic advantages of the latter. The advantages of gas- 
eous fuel become still more strongly apparent when we consider that 
in a very large number of cases the amount of heat which coal is 
capable of affording is but imperfectly utilized, and that, in fact, 
owing to the intermittent use of the heat, but a small proportion 
of the theoretically available fifty per cent, is ever attained. It is 
safe to say that for domestic use the cost of the Strong gas would 
be at most but fifty per cent, of the cost of coal fires, and in sum- 
mer even less. 

" The only other forms of gaseous fuel with which the Strong 
gas can be compared are coal gas and the Siemens gas. 

" While the theoretical heating effect of coal gas, viz, twenty- 
two thousand units, is about two and a-half times that of the 
Strong gas, the great cost of the former places it practically out of 
competition. 

"Concerning the Siemens gas we have the following data on 
authority of Percy * The average composition by volume of the 
gas at St. Gobian is, 

::= Metallurgy, Revised Edition, L, p. 528. I accept Percy's statement of the yield 
of the Siemens gas with great reserve. Except on the assumption that there has "been 
an enormous loss during the process of manufacture, his estimate is much too low. 
As the statement, however, appears never to have been contradicted, I have employed 
it in default of more exact data for comparison. 



278 COMBUSTION OF COAL, 



Hydrogen „ r 7.50 

Carbonic oxide 17.00 

Carbonic acid 6.58 1 

Nitrogen 69.00 

100.00 

and it possesses, according to Percy, the average specific gravity, 
0.78. One cubic foot at sixty-two degrees Fahrenheit, would there- 
fore weigh 0.059 pound. The theoretical heating effect deduced 
from the foregoing analysis is 1101.1 units of heat per pound. 

"According to Percy, one ton of coal, free from ash, will yield 
fifty-thousand cubic feet of gas. Assuming the coal to contain five 
per cent, of ash, one thousand cubic feet of the Siemens gas would 
require for their production forty-seven pounds of coal, and as one 
thousand cubic feet weigh 59.38 pounds, we have 59.38X1101.1 = 
G5,383.3 units as the heating power, compared with the 340,386 
units afforded by the nine hundred and forty cubic feet of the 
Strong gas obtained from forty-seven pounds of coal. If, there- 
fore, we assume that the Siemens gas has been made from coal at 
$1.50 per ton, and if we leave out of account the cost of labor, 
repairs and all other items of incidental expenditure, we have, 
as the cost of the 65,383 units of heat of the Siemens gas 3^ cents, 
while one thousand cubic feet of the Strong gas, costing seven 
cents, will yield 362,113 units, or, in other words, taking as the cost 
of the Siemens gas the cost of the coal required to produce it, and 
allowing for the Strong gas the inventor's estimate, deduced from 
actual experience, of the total cost of production, the cost of a 
given quantity of heat obtained from the Siemens gas is to that of 
the same quantity obtained from the Strong gas in the proportion 
of 2.5 to 1. 

" The theoretical elevation of temperature produced by the 
combustion of the Siemens gas is, as deduced from the foregoing 
analysis, 2,592 degrees Fahrenheit, or, with the air and gas at the 
initial temperature of 62° Fahr., the temperature of the flame 
would be 2,654° Fahr. 

" One cubic foot of the Siemens gas requires 0.58 cubic foot of 
air for its perfect combustion, and yields 1.46 cubic feet of pro- 
ducts of combustion, of which 1.39 cubic feet are permanent gases. 

" For every one thousand cubic feet of gaseous products of 
combustion from the Siemens gas, there are developed 44,648 units 
of heat. 



FUEL GAS. 279 



" For every one thousand cubic feet of products of com- 
bustion from the Strong gas, there are developed 119,035 units of 
heat. 

" Hence, for the production of a given quantity of heat, there 
is formed with the Siemens gas 2.68 times the volume of gaseous 
products that would result from the use of the Strong gas. 

INFLUENCE OF THE SPECIFIC HEAT OF THE PRODUCTS OF COMBUSTION 
OF THE STRONG GAS. 

" In the foregoing estimates, I have assumed that the products 
of combustion of the Strong gas have been entirely deprived of 
their available heat, as would be the case in a rational system of 
practice, wherein the waste heat of the fire gases is used to heat 
the blast, or, in the case of the generation of steam, the feed water 
for the boilers. 

"In the limited number of cases where this can not be done, 
other factors must be included in the calculation, whereby the 
result is to some extent modified, viz, the latent heat of vaporiza- 
tion of the water contained in the products of combustion, and 
the specific heat of the permanent gases therein. 

"This correction becomes of special importance in the consid- 
eration of the question of a direct comparison between the Strong 
gas and other forms of fuel, such as coal and the Siemens gas, in 
the combustion of which a much smaller amount of aqueous 
vapor is formed. 

"Selecting, for illustration, the simplest conditions under 
which the problem could present itself, we will take the case 
where the products of combustion leave the chimney at the tem- 
perature of two hundred and twelve degrees Fahrenheit. 

"In our previous study of the conditions of combustion, I 
have assumed that the fire gases have been cooled down to the 
normal temperature of sixty-two degrees Fahrenheit, the tempera- 
ture at which the air and gas were presented for combustion. 

" One pound of the Strong gas contains, 

Oxygen 0.0174 

Carbonic acid 0.0637 

Nitrogen 0.0880 

Carbonic Oxide 0.7097 

Hydrogen 0.0747 

Marsh gas 0.0465 

1.0000 

and requires for its perfect combustion 5.9052 pounds air, yielding 
i). 9052 pounds of products of combustion. On multiplying the 
weights of the several products of combustion by the number of 



280 COMBUSTION OF COAL. 



units of heat required to raise one pound thereof from 62° to 212° 
Fahr., we obtain the following result, viz: 

Nitrogen 4.6593 x (150 x .2240= 33.60) = 150.55 

Carbonic acid 1.4690 x (150 x .2164= 32 46)= 47.68 

Water 0.7769 x (150 x 1.0000 = 150.00) = 116.53 



6.9052 
Latent heat of the vaporization of the water 0.7769 x 966 = 750. 4S 



Heat units retained by fire gases at 212° Fahr 1,071.24 

Whence Ave have, 

Calorific equivalent of Strong's gas 8,798 units 

Latent heat of waste gases at 212° 1,071 units 

Utilized 7,727 units 

or, of the total heating power of the gas there is, 

Wasted 12.18 per cent. 

Utilized 87.82 per cent. 

100.00 

" Let us see how the Siemens gas behaves under similar condi- 
tions. One pound contains 

Nitrogen 0.7140 

Carbonic acid 0.1053 

Carbonic oxide 0.1752 

Hydrogen 0.0055 

1.0000 

and requires for its perfect combustion 0.6380 pound of air, yield- 
ing 1.6380 pounds of products of combustion. Proceeding, as before, 
we have, 

Nitrogen 1.2079 x (150 x .2240= 33.60) =40.59 

Carbonic acid 3806 x (150 x .2164= 32.46) = 12.37 

Water 0495 x (150 x 1.000 = 150.00)= 7.43 



1.6380 
Latent heat of vaporization of the water, 0.0495 x 966 = 47.82 

Heat units retained by fire-gases at 212° 108.21 

Whence we have, 

Calorific equivalent of Siemens gas 1101.1 

Latent heat of waste gases at 212° 108.2 

Utilized 992.9 

or, of the total heating power of the gas, there is, 

Wasted 9.82 per cent. 

Utilized 90.18 per cent. 



FUEL GAS. 281 



"On the assumption, therefore, that the water formed by com- 
bustion is allowed to escape as steam, at 212° Fahr., the per cent- 
age of loss of heating effect from the latent heat of the fire gases 
is theoretically slightly greater in the case of the Strong gas than 
in that of the Siemens gas. In practice, the unavoidably large 
excess of air required for the combustion of the Siemens gas would 
cause the comparison to result decidedly in favor of the Strong gas. 

"The application of water-gas in metallurgy is not new. We 
are. on the contrary, informed by Percy, * that the gas produced by 
the old and costly method of causing steam to re-act on coke in 
cast iron retorts was seen by him in operation for several years, at 
the Oldbury furnaces, near Birmingham, and that its use had been 
commenced in the Yorkshire blast furnaces. 

" The special advantages of the Strong gas for use in metal- 
lurgy are, apart from the question of economy, the high and easily 
regulated temperature it affords, and the relatively small volume of 
products of combustion compared with the heating effect. It is> 
in fact, the most concentrated form of gaseous fuel hitherto attain- 
able for this application. 

APPLICATION OF THE STRONG GAS FOR ILLUMINATING PURPOSES. 

" The Strong gas possesses two very valuable attributes as 
regards its application for illuminating purposes, either when used 
alone after charging it with illuminating hydrocarbons or as a 
diluent for very rich coal gas — the temperature of the flame, 
namely, and the heating power. As I have already shown, the 
flame temperature is some nine hundred degrees Fahrenheit 
higher than that of coal gas. while the quantity of heat evolved 
during combustion is to that from coal gas in the proportion of one 
to 2.5. This proportion would, of course, be somewhat changed 
after the gas had been charged with illuminating substances, but 
in any event, with equal illuminating power, it will prove compara- 
tively free from the tendency to heat the air of the rooms in 
which it is burned, which is one of the grave objections to ordi- 
nary coal gas. 

" The superior freedom of the Strong gas from sulphur is an 
extremely valuable property for illuminating purposes. 

" The question naturally arises here, whether the use of a gas 
containing, as shown by analysis, as much as thirty-six per cent, of 
carbonic oxide, and which, under certain circumstances, might pos- 

* Metallurgy, 1861, I., p. 203. 



282 COMBUSTION OF COAL. 



sibly contain from forty to forty-five per cent., would not be attended 
with danger to the health of the consumer. 

" Leaving out of account the fact that there is even now some 
difference of opinion as to the precise nature and extent of the 
constitutional effects of air impregnated with a small proportion of 
carbonic oxide, it would be obviously absurd to base any estimate 
on the poisonous nature of the pure gas, or even on the proportion 
contained in the Strong gas. The question can only be decided by 
comparison with our previous experience with other illuminating 
gases of known composition. 

" Were carbonic oxide the only poisonous ingredient in coal 
gas there might appear to be some foundation for the reasoning of 
the opponents of such gases as the Lowe gas, that if coal gas, which 
may contain as much as fifteen per cent, of carbonic oxide, be poison- 
ous, a gas which may'contain thirty per cent, must necessarily be 
twice as much 'so. Unfortunately for this chain of reasoning, car- 
bonic oxide is not the only, or even the most, poisonous ingredient 
in coal gas. The heavy hydrocarbons, especially the vaporized 
tarry substances, may produce, when mixed even in slight propor- 
tion with the air, vertigo, insensibility and even death. According 
to Jacobs " the contents of as much as three (3) per cent, of coal 
gas in the air of a room is fatal to human life. If we accept the 
still smaller proportion of one per cent, of carbonic oxide as the 
minimum quantity required to produce an injurious effect, then 
fully three per cent, of such a gas as the Lowe gas would have to be 
present, whence it follows that the amount of such gas necessary to 
produce an injurious effect would practically amount to a fatal dose 
of ordinary coal gas. 

" The absurdity of claiming that a gas containing as much as 
twenty-five to thirty per cent, of carbonic oxide is necessarily dan- 
gerous, will best be apparent from the consideration of the amounts 
contained in wood gas — a material largely used wherever the relative 
cost of wood and coal renders it economically advantageous. I give 
below the proportions of carbonic oxide found in different kinds of 
wood gas: 

KIND OF GAS. CARBONIC OXIDE. ANALYST. 

Not specified 61.79 Pettenkofer. 

Crude 37.62 Pettenkofer. 

Crude 28.21 Pettenkofer. 

From Beech Wood 41.94 Rcissig. 

From Birch Wood 35.99 lleissig. 

From Pine Wood 38.25 lleissig. 

From Turf 20.33 lleissig. 

* Quoted iu Stohmann-Muspratt's Chemie, 3d Ed., IV., 623. 



FUEL GAS. 283 



" In the year 1862, the following European towns were lighted 
with wood gas, viz, Coburg, Wurzburg, Darmstadt, Giessen, Zurich, 
St. Gall, Schaffhausen, Aarau, Lucerne, Regensburg, Landshut, 
Erlangen, Ulm, Kempton, Linz, Chur, Freiburg (in Switzerland), 
and many others. I have been unable to find that the question of 
possible danger from the presence of carbonic oxide in wood gas has 
ever been raised. 

" The objections to water gas in general on account of its contents 
in carbonic oxide are based on an entire misconception of the 
meaning of the reports of the eminent scientific men who were 
called to pronounce upon the question of its safety in France. 
The French report was unfavorable for the following reasons : 

" The gas was not saturated with illuminating hydrocarbons 
and was consequently inodorous; it was not of itself luminous, but 
was employed to heat to intense whiteness small cages of platinum, 
which were suspended in the flame and furnished the luminous 
body. Being inodorous, the escape of the gas could not have been 
detected, hence the dangers arising from accidental leakage were 
excessive. If the Strong gas be made luminous, it must, like the 
Lowe gas, receive a strong and characteristic odor. Herein lies, 
also, the only element of safety in the use of ordinary coal gas, 
loooo °f which can be detected in air by its odor. Coal gas, if ino- 
dorous, would in all respects be as dangerous for domestic use as 
pure carbonic oxide gas. 

"I have no hesitation in stating as my opinion, that 'water- 
gas,' either the Lowe gas or the Strong gas, when properly 'car- 
bureted,' is in all respects as safe for household use as ordinary 
coal gas. 

"I can not better conclude my report than by stating my 
entire concurrence in the opinion of the greatest living authority 
in chemical technology, Rudolph Wagner,* who, after alluding to 
the lack of success of the previous attempts to introduce water- 
gas, owing to imperfect apparatus, says: 'Nevertheless, water-gas 
still appears to us to be the illuminating gas of the future.' 

" Respectfully submitted by your obedient servant, 

"Gideon E. Moore, Ph. D. 

"Jersey City, January 22, 1878. 

"Tb the American Gas-fuel and Light Company, New York.' 1 



Jahrcsbcricht der Chemischen Technologie, 1874, p. 991. 



CHAPTER XVII. 

UTILIZING WASTE GASES FROM THE FURNACE. 

Waste Products — Magnitude of the Loss — Siemens' Regenerative 
Gas-Furnace. 

The waste products of furnaces may be divided into 
two classes : 

1. The escape of gases in which combustion has 
been incomplete. This is confined almost exclusively to 
carbonic oxide, a combustible gas, formed in the furnace 
by a too little supply of oxygen at the time, or during 
the process of combustion. 

2. The escape of heated products which may in 
themselves be incombustible, but having passed their 
point of application, are rendered unavailable to the pur- 
poses for which they were generated, and are thus a 
source of loss. 

In blast furnaces, waste gases are made to serve a 
useful purpose in generating steam, heating the blast, 
etc.; in puddling furnaces, by heating a steam boiler, 
which is usually placed directly over the furnace; and 
in many other ways these waste gases are partially 
utilized. To show the necessity for utilization, and the 
magnitude of this loss in case of neglecting to do so, 
was clearly stated in a lecture given by Dr. Siemens, on 
Fuel (1873), in which he says: "Taking the specific 
heat of iron at .114, and the welding heat at 2,900° 
Fahr., it would require .114 X 2,900=331 heat units 



SIEMENS' REGENERATIVE GAS-FURNACE. 285 

to heat one pound of iron. A pound of pure carbon 
developes 14,500 heat units, a pound of common coal, say 
12,000; and, therefore, one ton of coal should bring 
thirty-six tons of iron up to the welding point. In an 
ordinary re-heating furnace, a ton of coal heats only 
1| ton of iron, and, therefore, produces only -~ part of 
the maximum theoretical effect. 

"In melting one ton of steel in pots two and a-half 
tons of coke are consumed, and taking the melting 
point of steel at thirty-six hundred degrees Fahren- 
heit, the specific heat at .119, it takes .119X3,000 
= 428 heat units to melt a pound of steel, and tak- 
ing the heat-producing power of common coke also 
at twelve thousand units, one ton of coke ought to be 
able to melt twenty-eight tons of steel. The Sheffield 
pot steel melting furnace, therefore, only utilizes -^- part 
of the theoretical heat developed in the combustion." 

These facts led Dr. Siemens as early as 1846 to con- 
sider the practicability of storing this waste heat and 
utilizing it again and again. In this he was successful, 
and his regenerative furnace marks an era in the util- 
ization of waste gases. 

Siemens' Regenerative Gas-furnace — The construction 
of this furnace is shown in plate IV; a description 
and its mode of operation are clearly set forth in the 
specification of his American patent given below: 

" In the accompanying plate of drawings, in which 
corresponding parts are designated by similar letters, 
figure 1 is a partial longitudinal vertical section of the 



286 COMBUSTION OF COAL. 

furnace. Figure 2 is a horizontal longitudinal section, 
showing the relative position of the air and gas flues. 
Figure 3 is a transverse vertical section of the furnace 
through the cave A. Figure 4 is a transverse vertical 
section through the air flues. Figure 5 is a longitudinal 
elevation. 

" The regenerative gas-furnace, as shown in the 
drawings, is built of fire-brick or other suitable 
refractory material, and consists of the four regen- 
erators with the flues and valves, and the heating- 
chamber, where the metallurgical operations are car- 
ried on. 

" The four regenerators are arranged in pairs, and 
vary in size, the smaller being used for the passage of 
gas, and the larger for that of air, their proportions 
being in the ratio of two to three. Approximately, 
these ratios correspond to the quantities of gas and air 
required to insure complete combustion in the heating- 
chamber. The walls of the regenerators are 
built of fire-brick or other suitable refractory mate- 
rial, closely laid and white-washed, or other- 
wise made gas-tight, so that no leakage may 
take place from one chamber to another. These 
chambers are filled with refractory material, by prefer- 
ence fire-brick, stacked loosely together, and each regen- 
erative chamber has its own separate flue at the base, 
communicating with the valves by which the gas and 
air enter, or the products of combustion pass out, while 
from the top or side of each regenerative chamber a 
series of flues pass upward and communicate with the 



SIEMENS' REGENERATIVE GAS-FURNACE. 287 

heating chamber ; and I prefer to cause the air to enter 
the heating chamber above the gas, as by its superior 
specific gravity at equal temperatures it tends to sink 
through the gas, and thus an intimate mixture and more 
perfect combustion is obtained. The entering or issuing 
gaseous currents pass through valves, which are shown 
in a: in figure 3. 

" The heating chamber where the metallurgical pro- 
cesses are carried on, has its roofs and sides constructed 
of highly refractory materials, such as best silica or 
Dynas bricks. The bed is usually made of sand. 

" Below the center of the furnace is an open cave, A, 
through which air freely circulates, and rises through 
openings into the air-space below the melting chamber 
and behind the bridges, whereby a perfect cooling of 
the sides of the melting chamber is effected. This cave 
serves, moreover, as a receptacle for any metal which 
may break through the sides or bottom of the melting 
chamber, whence it can be removed at leisure, without, 
meanwhile, encumbering the ventilating spaces around 
the melting chamber. 

"On first lighting the furnace, the gas passes 
through the proper valves and flues into the bottom of 
regenerator chamber c, while the air enters through 
corresponding valves and flues into the regenerator 
chamber E, which should be about one-half larger than 
the gas regenerator chamber c. The currents of gas 
and air, both quite cold, rise separately through the 
regenerators c and JE, and pass up through the series of 
flues G G G G G and F F F F F, respectively, into 



288 , COMBUSTION OF COAL. 

the furnace above, where they meet and are lighted, 
burning and producing a moderate heat. Each air- 
port rises from its regenerator behind the corresponding 
gas-port, and is projected into the furnace over such 
gas-port, it being important that the air-port should 
overlap the gas-port on both sides. Great solidity of 
brick work and perfect combustion is thereby attained. 
" The products of combustion pass away through a 
similar set of flues at the other end of the furnace, into 
the regenerator chambers c' E, which are not shown in 
the drawings, but are symmetrical, both in construc- 
tion and arrangement, with the chambers c E, already 
described. The products pass from thence, through 
properly-constructed flues and valves, to the chimney- 
flue. The waste heat is thus deposited in the upper 
courses of open fire-brick work, filling the chambers 
c' E, and heats them up, while the lower portion and 
the chimney-flues are quite cool; then, after a suitable 
interval, the reversing flaps — through which the air and 
gas are admitted or withdrawn from the furnace — are 
reversed, and the air and gas enter through those regen- 
erator chambers E c\ which have been just heated by 
the waste products of combustion, and in passing up 
through the checker-work they become heated, and 
then, on meeting and entering into combustion in the 
furnace D, they produce a very high temperature, the 
waste heat from such higher temperature of combustion 
heating up the previously cold regenerators c E, to a 
corresponding higher heat. Thus an accumulation of 
heat and an accession of temperature is obtained step 



C.W. SIEMENS. 

REGENERATIVE GAS FURNACES. 



FIG.4. 




SIEMENS' REGENERATIVE GAS-FUNNACE. 289 

by step, so to speak, until the furnace is as hot as 
required. The heat is, at the same time, so thoroughly 
abstracted from the products of combustion by the 
regenerators, that the chimney-flue remains compara- 
tively cool. 

"The command of the temperature of the furnace,, 
and of the quality of the flame, is rendered complete by 
means of gas and air-regulating valves, and by the chim- 
ney damper." 



(20) 



CHAPTER XVIII. 

A. PONSAED'S PEOCESS AND APPAEATUS FOE GENEEAT- 
ING GASEOUS FUEL. 

The following is a copy of the specifications of 
Auguste Ponsard, Paris, France, describing in detail his 
process and apparatus for generating gaseous fuel : 

"It is the object of rny invention to increase the 
production of carbonic oxide from a given quantity of 
fuel; to produce this gas at the highest possible temper- 
ature, so as (without passing it through any cuperator or 
regenerator) to introduce it at the highest possible tem- 
perature to the furnace in which it is to be consumed; 
to support the combustion of this gas by the introduc- 
tion to the furnace of air previously heated by the 
waste products of combustion, and to simplify the 
apparatus required for the production and consumption 
of gaseous fuel, while attaining a higher heat than has 
been heretofore obtained therefrom. 

" Previous to my invention, when the highest heats 
from gaseous fuel have been required it has been neces- 
sary that the temperature of the gas should be raised 
before its introduction to the furnace for combustion, 
not only because it could not be produced at a suffi- 
ciently high temperature, but because much of its orig- 
inal heat had been lost in its passage from the producer 
to the furnace, in most instances widely separated. In 
that system the expense of the apparatus is increased, 



ponsard's process and apparatus. 291 

not only by the cost of the separate structures, but by 
the means required to connect them; and as the more 
volatile particles of the gas are deposited in passing 
from the producer toward the furnace, and in restoring 
the heat by the recuperator the gas deposits another 
portion upon the recuperator, this operation is attended 
with a constant waste of fuel. 

"My invention consists, first, in supporting the com- 
bustion of the gas-producing fuel by supplying it with 
a continuous current of highly-heated air, and so regu- 
lating this supply as to control the activity of the com- 
bustion ; second, in defining the traverse of this air, and 
the gas produced thereby, so that the gas shall pass off 
at the highest temperature ; and, third, in effecting an 
intense combustion by the introduction to this gas, as it 
passes to the furnace, of air previously heated by the 
waste products of combustion. 

"At the ordinary temperature of the atmosphere, the 
air and the fuel for the production of carbonic-oxide 
gas will not combine with sufficient rapidity to produce 
sensible heat. The rapidity of their combination and 
the intensity of the resultant heat are probably in pro- 
portion to the temperature of the two, respectively, 
previously to their combination. 

"In gas-producers, as heretofore constructed, the gas- 
producing fuel performs two functions — first, to heat 
the air and the fuel to a sufficient temperature to con- 
tinue an active combustion, producing carbonic-acid gas, 
and, second, to heat the remaining fuel to such a degree 
that a slower combustion without flame will take place, 



.292 COMBUSTION OF COAL. 

In which the carbonic acid should take up another charge 
of carbon and become carbonic oxide; but in all such, 
producers a portion of the carbonic acid will pass 
through without taking up another charge of carbon, 

"KoWy if the air which is to support the primary 
combustion should be so heated that none of the heat 
from the fuel would be required for the primary condi- 
tions, the carbonic acid would be produced at a much 
higher temperature, and its liability to pass through the 
remaining fuel without taking up another charge of 
carbon would be diminished, so that the product of 
carbonic oxide from a given quantity of fuel would be 
greater than has heretofore been obtained. Moreover, 
the air coming to the fuel heated, instead of to be 
heated, not only promotes the combustion of the fuel 
and the production of carbonic .oxide, but it also inten- 
sifies the temperature of this gas by the direct contribu- 
tion of heat instead of abstracting it, as heretofore. 

" It must be borne in mind that the consumption of 
fuel at any temperature, however high, will be propor- 
tioned to the quantity of air admitted to combine with 
it, so that, while the quantity of air admitted is kept 
within the limits which must be observed to prevent a 
too active combustion, the result obtained will be an 
increased quantity of carbonic oxide at a higher tem- 
perature than has heretofore been possible. 

"In the accompanying drawings I have shown an 
improved apparatus, in which the operation of my 
invention is exemplified. 



293 



"Figure 1 represents a vertical longitudinal section 
of my improved apparatus applied to a heating-furnace, 
line of section A B, figure 2. Figure 2 is a horizontal 
section thereof, following the line C D, figure L Fig- 
ure 3 is a vertical transverse section on the line a b, fig- 
ure 1. Figure 4 is a vertical transverse section on the 
line 1 J, ; figure 1. Figure 5 is a vertical transverse section 
on the line e d, figure 1. Figure 6 represents in detail, 
and upon an enlarged scale, the hollow bricks which I 
use, and the manner in which they are put together in 
the recuperator. The principal feature in their con- 
struction is the recessed ends s, which, when in position, 
as at s 1 s', form chambers in which fire-clay can be 
packed, so as to form a key to hold the structure 
together, as well as an interruption to the passage of 
gas and air at the joint. This general arrangement of 
the recuperator is the same as described in letters pat- 
ent of the United States ¥o. 130,313, granted to me 
August 6, 1872. 

"The gas-producer consists of a rectangular cham- 
ber, a, the lower part, b, of which is greatly contracted, 
in order that the residuum of the fuel (cinders and slag) 
in the contracted space, b, may be easily removed with 
stoking-irons. 

" The fuel is charged through the hopper and clap- 
valve e, and the arch d serves to limit its height in 
chamber a. The fuel is supported by the hearth p^ 
upon which the cinders and slag will accumulate, and 
from which they may be removed, as hereinafter 
described. The hot air is brought from the recuperator 



294 COMBUSTION OF COAL. 

i to the front of the producer through the conduit e 9 
and reaches the fuel through the opening /, which 
takes up nearly the whole width of the chamber a. 

" The ash-pit g can be closed by means of vertically- 
sliding doors of sheet-iron, A, which are raised by means 
of counter-weights; or it may remain open if the press- 
ure of the hot air entering the producer is not great 
enough to force back the gas through this part of the 
apparatus. To prevent the loss of gas which might 
result from its driving back under pressure, the sliding 
doors may, after each clearing of the pit, be luted with 
ashes, earth or sand. 

"In the front wall of the contracted portion b of the 
producer, above the arch of the ash-pit, openings j are 
provided, through which stoking-irons may be intro- 
duced to lift and stir the fuel; and to remove the ashes 
and slag to the lower part of the apparatus through the 
openings J, bars may be inserted to sustain the fuel 
above the hearth, and within the producer, while the 
ashes, cinders or slag are being removed from the 
hearth p beneath the bars. In the side walls of the 
producer are also provided openings k, which, together 
with the sight-holes I, arranged in the arch, allow the 
introduction of stoking-irons to compact the fuel, and 
to break up any arches that may be formed by the 
agglomeration of coal, especially if a rich kind of coal 
is used. The recuperator i is divided into two parts, 
one of which serves to heat the air required to support 
combustion in the producer, and the other to heat the 
air for the combustion of the gas as it enters the fur- 



295 



nace by means of the passage m. This division of the 
recuperator into two distinct parts may be made com- 
plete or partial only; in other words, they may be 
entirely separated by a solid wall, or the transverse air- 
passages only may be filled up (divided) by solid bricks, 
leaving the passages for products of combustion in com- 
munication. This latter disposition is represented in 
the drawing. 

"Whatever arrangement may be adopted, independ- 
ent valves must be placed before each group of ori- 
fices for the admission of air into the divided recup- 
erator, to regulate the quantity of air admitted to the 
producer, as well as to the furnace. In the drawings, 
the position of these valves is represented at n, figure 1, 
in the rear of the recuperator, and they are operated by 
screwed rods n f and hand- wheels o. 

" With a view to obtain the maximum advantages of 
my improved system hereinbefore described, I contem- 
plate varying, under varying circumstances, the con- 
struction of the producer, with the view, in all cases, to 
admit the air above the hearth, to define its traverse 
through the fuel, and to carry off the carbonic oxide 
from that section of the producer where this gas is the 
hottest. 

"In the disposition represented in figures 7 and 8, the 
gas-producer consists of a vertical chamber, a (which is 
charged with fuel by means of two ordinary valve-boxes, 
6'), the lower portion of which presents openings upon 
opposite sides, by means of which the cinder and ashes 
may be removed. To this end the lower portion of the 



296 COMBUSTION OF COAL. 

space a terminates in two inclined planes, c, extending 
down to a certain distance above the ground, in such 
manner that raking-bars may be easily inserted into the 
openings thus provided, to remove and loosen the ashes 
and cinders accumulating in this portion of the pro- 
ducer. In this disposition the conduit b for the out- 
going gas is placed lower than shown in the drawings, 
figures 1 to 5, and is elevated above the plane of the 
conduit c, for the admission of air, so that the air will 
traverse the fuel in a slightly-ascending plane. 

"Figures 9 and 10 represent a gas-producer, a, which 
from the top to its base presents the form of a frustum 
of a pyramid. This is varied in width according to the 
nature of the combustible employed. In this disposition 
the conduit b of the out-going gas is placed at the same 
height with, or even a little lower than, the conduit c, 
supplying the hot air, and the two orifices of these con- 
duits are fitted with a grating, d, forming a part of the 
inclosure of the space a. This grating is constructed of 
refractory pieces (as bricks), the shape of which may 
vary, while they are so disposed as to leave sufficient 
sectional area for the air and gas. These bricks are 
simply built up without the interposition of any mortar, 
so that they may be easily replaced (when deteriorated) 
through the openings e, provided in the two parallel long 
sides of the producer. The lower part of the apparatus 
is closed by loose walls /, which are withdrawn to 
remove the ashes produced by combustion, the coal 
remaining supported during this time by the grate g, 



PONSARD S PROCESS AftD APPARATUS. 297 

the removal of a few bars of which will allow the cin- 
ders accumulated in this part of the producer to fall. 

"Figures 11 and 12 represent diverse arrangements 
of the gratings d, designed to prevent the coal from 
falling out laterally into the passages b and c, for the 
outlet of gas and inlet of air. In figure 11 the grating is 
formed by thin bricks A, laid fiat upon bearers i, leaving 
passages between these shallow enough to prevent the 
coal from sliding outward. In figure 12 the grating is 
formed of hollow bricks j, arranged in quincunx, or 
simply superposed, so as to leave numerous passages for 
the gas and air, while they prevent the coal from 
obstructing the passages b and c. 

"It is evident that the forms and dispositions of 
these pieces of refractory clay may be greatly varied 
without inconvenience, provided they are arranged to 
be easily withdrawn and replaced through the openings 
e, when they become injured from use. 

" Figures 13 and 14 represent a producer in which 
only the orifice b for the outlet of gas is closed by a 
grating, d, disposed in steps. The other side where the 
air is admitted is inclined, and if a similar inclination is 
given to the grating, the layer of coal traversed by the 
air is about equal at all points. 

" Figures 15 and 16 represent a producer, in which 
the hot air enters the fuel from above, and the gas may 
go out through one side or both sides of the apparatus. 
The drawing represents two outlets, b, and I have also 
increased the width of this part of the chamber, so 
that the layer of fuel traversed by the air may be 



298 COMBUSTION OF COAL. 

as uniform as possible. It will also be observed that I 
have provided in the masonry offsets, k, into which 
the fuel may slide, and which will tend to prevent 
the hot air entering by the passage c from follow- 
ing the inclosure of space a, and compel it to traverse 
the fuel before reaching the outlets b for the gas. 

"The air which supports combustion in the gas-pro- 
ducer acquires the force necessary to enter the producer 
from the heat which it receives in passing through the 
recuperator; but it may also be injected either by means 
of a blower, or by a jet of steam, or by a blast-engine of 
any kind. Of these methods I prefer to employ the jet 
of steam, because the steam in passing through the fuel 
is decomposed, and produces a gas rich in carbon. I 
obtain this result, when the air is not forced, by admit- 
ting into the lower part of the recuperator a small 
quantity of water by means of an iron tube which is 
inserted into the air-inlet, as shown in figure 1. This 
water is vaporized in the iron tube, and escapes as 
steam into the recuperator. 

"I am aware that a gas-producer has been described, 
in the operation of which previously-heated air was 
introduced to support the combustion of the gas-pro- 
ducing fuel. Two regenerators and conduits alternately 
carried a current of air to, and a current of gas from, 
the producer, and these currents were reversed for the 
purpose of heating the air, but with the effect of cool- 
ing the gas. Each conduit and regenerator, therefore, 
was alternately filled with gas or with air, so that with 
each reversal of the currents, the gas contained in the 



A.PONSARD. 
PROCESS & APPARATUS FOR GENERATING GASEOUS FUEL. 



El D 








ponsard's process and apparatus. 299 

one was returned through the fuel, while the air con- 
tained in the other was delivered into the flue leading 
to the furnace, where it would mix with and deteriorate 
the quality of the gas. In this case the length of the 
flue to the furnace permitted an admixture; but with a 
delivery directly into the furnace, such as I contem- 
plate and set forth, the flame would be extinguished, 
and its place supplied by a blast of heated air alone at 
each alternation, which would not only diminish the 
heat, but oxidize the contents of the furnace." 



INDEX. 



PAGE 

Acid, sulphurous in smoke 102 

Air 25 

Air, admission of above the fuel 113, 142 

Air, .. I Eu( 1....153, 15G 

Air, admission of cold above the fire 161 

Air, composition of 26 

Air, distribution of in the furnace 141 

Air, diathermacy of 34 

Air, difficulty in boating or cooling 134 

Air, effect of heated 130 

Air, heated for draft 215 

Air, physical properties of 30 

Air, quantity affecting temperature 121 

Air, required for combustion 126, 132 

Air, temperature at high altitudes 32 

Air, transparency of 34 

Air, weight of 30 

Albertite, in gas making 63 

Alcohol, flame of 115 

Alumina, in ashes 1G9 

Ammonia 33, 91 

Analysis of coal 81 

Anthracite coal 78 

Anthracite, action in the fire 79 

Anthracite, rate of combustion 119 

Apparatus for gas analysis 174 

Area of chimneys 136 

Ashes 81 

Ashes, analysis of 109 

Ashes and clinkers 168 

Ashes, color of 170 

Atmosphere 25 

Atmosphere of the coal period 16 

Atmosphere, physical properties of 30 

Atmosphere, weight of 31 

Atoms 3 

Atomic weights 7 

Atomic weights aud specific heat 196 

Atoms and molecules 5 

Benevines, on flame 116 

Berthier, on heated air 130 



PAGE 

Bitumen, not in coal , 53 

Bituminous coal 52 

Bituminous coal, analysis of 55, 60 

Bitumin soal, properties of 53 

Bituminous coal, rate of combustion 119 

Bituminous coal, Illinois 55 

Bituminous coal, Indiana 56 

Bituminous coal, Kentucky 59 

Bituminous coal, Ohio 60 

Bituminous coal, Pennsylvania 57 

Blandy, V. Z., analysis by 55, 56 

Blochman on flame 115, 116 

Block coal 64 

Boetius' furnace 129, 134 

Boiler and chimney connections 140 

Boiler corrosion 163 

Boulton and Watt on chimney heights.. 140 

Boyle's law 30 

Bridge-wall, McMurray's 153 

Brown coal and lignite 42 

Bunsen burner, flame in 114 

Burning smoke 160 

Caking coals 61 

Calorie 206 

Calorific power of coal 182, 184 

Calorific power of Strong's gas 274 

Calorimeter, Favre and Silberman 179 

Calorimeter, Thompson's 188 

Candle power explained 62 

Cannel coal 73 

Cannel coal, analysis of 74, 76 

Cannel coal, in gas making 63 

Cannel coal, Indiana 75 

Cannel coal, Kentucky 74 

Cannel coal, Pennsylvania 74 

Capacity for heat 199 

Carbon 87 

Carbon and oxygen 88 

Carbon, air required for 132 

Carbon, how it spontaneously ignites.... 229 
Carbon, molecular weight of 6 



302 



INDEX. 



PAGE 

Carbon, specific heat of 88 

Carbon, temperature of combustion of... 121 

Carbon, units of heat in 1S2 

Carbonic acid 158 

Carbonic acid in atmosphere 33 

Carbonic acid in plants 20, 22 

Carbonic oxide 158 

Carbonic oxide, effect of on health 282 

Carbonization of coal 65 

Carbureted hydrogen 90 

Charcoal 37, 38 

Chemical action 100 

Chemical affinity 108 

Chemical analysis 81 

Chemical and mechanical changes 3 

Chemical and physical changes 2 

Chemical properties of bodies 2 

Chemical separation, energy, of 104 

Chevandier, M. Eugene, quoted 37 

Chimneys 210, 217 

Chimneys, draft in 136 

Chimneys, height of .137, 139, 140 

Clinkers ; 168 

Coal, analysis of 81 

Coal, anthracite 78 

Coal, bituminous 52 

Coal, brown 42 

Coal, caking 61 

Coal, cannel 73 

Coal, carbonization of 65 

Coal, classification of 35, 52 

Coal, combustion of 106 

Coal, conditions necessary to burning 108 

Coal-dust fuel 233 

Coal, elementary analysis 84 

Coal, elements found in 7 

Coal, evaporative power of 191 

Coal, experimental calorific power of 186 

Coal, formation, area of in the U. S 15 

Coal, fusion of 1 

Coal, free burning 03 

Coal, for gas 61 

Coal gas, composition of 91 

Coal, Indiana block 64 

Coal, molecules of 2 

Coal, non-coking 61, 64 

Coal, parrot 74 

Coal, phosphorous in 85 

Coal, physical properties of 1 

Coal, products obtained from 94 

Coal, proximate analysis S3 

Coal, proximate constitution of 184 

Coal, quantity of gas in „ 26 



PAGE 

Coal, rate of combustion 118, 119 

Coal, required for good coke 70 

Coal, semi-anthracite 77 

Coal, semi-bituminons. 76 

Coal, spontaneous ignition of 226 

Coal, sulphur in 85 

Coal, theoretical calorific power 182 

Coal, vegetable origin of..... 16, 21 

Coke 65 

Coke, Connellsville... 65 

Coke, experiments on 66, 70 

Coke, from lignites 43 

Coke, kind of coal required for a good.... 70 

Coke, manufacture of in England 71 

Coke, quality affected by temperature... 66 
Coke, quantity produced in gas works.... 63 

Coking, heat developed in 73 

Coking, loss in 72 

Color of ashes 170 

Color of leaves due to sunlight 21 

Combustion 98 

Combustion, air required for 127 

Combustion, available heat of 123 

Combustion, and hot air 128, 130 

Combustion, and ignition 110 

Combustion, andlight 110 

Combustion,' conditions necessary to 109 

Combustion, in reverberatory furnaces.. 131 

Combustion, nature of 105, 107 

Combustion, of coal and coke 215 

Combustion, products of 159 

Combustion, rate of 117 

Combustion, table of heat units 180 

Combustion, table of temperatures 123 

Combustion, theory of 107 

Connellsville coke Qo 

Cornut, M 166 

Corrosion of boilers 163, 166 

Cost of makiug water gas 277 

Cox, E. T., analysis, methods of 82 

Cox, E. T., analysis, bituminous coal, 55, 59 

Cox, E. T., analysis, cannel coal 75 

Cox, E. T., analysis, lignites 44, 50 

Cox, E. T., experiments in coking 67 

Crampton'sexper'ts with powdered fuel, 238 

Davy, Sir H., on flame 114 

Definite proportions 101 

Deflectors in locomotives 128 

Degraded energy 24 

Diffusion in gassesand liquids 3 

Doors for furnaces 162 

Doville, M 163 

Draft, artificial 213 



INDEX. 



303 



PAGE 

Draft for different fuels 141 

Draft in chimneys 136 

Dynamical theory of heat 195, 204 

Elementary analysis of coal 84 

Energy 11 

Energy, dissipation of 22 

Energy of chemical separation 104 

Energy of fuel 15 

Energy, not reversible 23 

Energy, transmutation of 13 

Energy, types of 11 

English coals, rate of combustion 118 

Equivalent evaporation 192 

Equivalents, law of 102 

Equivalent numbers 5, 103 

Evaporation, latent heat of 202 

Evaporation per pound of fuel. ..157, 191, 193 
Explosion ill 

Fan blast 162 

Favre and Silberman 178 

Fire, temperature of 120 

Firing 161, 211, 218 

Flame Ill 

Flame and cold bodies 117 

Flame, appearance of 113 

Flame of hydrogen 114 

Flame, luminous 114 

Flame, temperature of gas 274 

Flame under pressure 115 

Foot pound 11 

Frankland on flame 115 

Free burning coal 65 

Fuel 35 

Fuel, energy of 15 

Fuel, mixture for calorimeters 190 

Fuel, products of carbonization 36 

Fuel, specific heat of 200 

Fuel, thermal power of 178 

Fuel, waste of 284 

Furnace defined 123 

Furnace doors 143, 14S, 162 

Furnace draft 136 

Furnace, efficiency of 123 

Furnace, losses in 124 

Furnace, requisites of 209 

Fusion, latent heat of 202 

Gas, advantages of as a fuel 257 

Oas, analysis 172 

Gas coal 61 

Gas coke 66 

Gas from water 260 

Gas furnaces, hot air in 129 



PAGE 

Gas from a ton of coal 62 

Gas, standard of Illumination 62 

Gas, sulphur in 92 

Gas, Strong's; a report on 271 

Gaseous fuel 254 

Gases, cooling of 212 

Gases, specific heat of 197 

Gases, table of heated 13S 

Gases, temperature of escaping 141 

Gases, volatilization of, from coal 212 

Gases, weight of, escaping 139 

Geisenhcimer's hot blast 129 

Gorman, W., gas furnace 130 

Grahamite, in gas making 63 

Grates, length of 161 

Grates recommended 172 

Grates, size of .»... 14<> 

Grothe's cupola 129 

Gruuer, Professor, quoted 267 

Gunpowder 99 

Hanet-Clery, M 162 

Hartford Steam Boiler Ins. Co 156 

Heat 195 

Heat, absorption of by forests 20 

Heat, action of on clinkers 171 

Heat, a form of energy 23 

Heat, developed by chemical action 178 

Heat, developed in coking 73 

Heat, generated by friction 14 

Heat, generated by impact 14 

Heat, how available 124 

Heat, latent 201 

Heat, lost in furnaces 216 

Heat, of combustibles, table of 180 

Heat, of combustion 107 

Heat, required in a puddling furnace 285 

Heat, required to melt steel 285 

Heat, theory of 195 

Heat, transferof 23 

Heated air and chemical action 131 

Heated air for combustion 128 

Heumann's experiments on flame 116 

Hoffman's kiln 129 

Horse power l] 

Howatson's furnace 130 

Hydrogen 89, 158 

Hydrogen, as a unit 5, 103, 197 

Hydrogen and nitrogen 91 

Hydrogen, atomic and molecular wghts, 5 

Hydrogen, burning of 90 

Hydrogen, flam'} of 114 

Hydrogen, gas from water 91 

Hydrogen, liquid 89 



304 



INDEX. 



PAGE 

Hydrogen, quantity of in water 90 

Hydrogen, solid 89 

Ignition and combustion 110 

Irish peat 40 

Ireland's cupola 129 

Iron, action of sulphur on 167 

Iron in ashes 169 

Iron pyrites 170 

Iron, sesquioxide of 170 

Isherwood on draft area ±37 

Johnson, analysis of coal 74, 77, 80 

Joule, Dr 204, 205 

Kane, Sir Robert, quoted 40 

K stner, Chailos 165 

Kilogrammetre 11 

Kinetic energy 11 

Knapp's experiments on flame 115 

Krigar's cupola 129 

Lamine, M 167 

Latent heat 201 

Latent heat of evaporation 202 

Latent heat of fusion 202 

Law of equivalents 102 

Law of gaseous volumes 8 

Levette, G. M., experiments on coke 67 

Light and combustion 110 

Light, effect of on plants 21 

Light produced by combustion 107 

Lignite 35, 42 

Lignite, Arkansas 48 

Lignite, Colorado 47 

Lignite, Foreign 51 

Lignite, Kentucky 44, 49 

Lignite, Texas 50 

Lignite, Vancouver's Island 46 

Lignite, Washington Territory 45 

Lignite and brown coal 42 

Lignite as a fuel 43 

Lignite, calorific power of 187 

Lignite coke 43 

Lignite, water in 44 

Liquefaction of hydrogen 89 

Liquid fuel 245 

Lime, incandescence of 110 

Lime, quantity of to purify gas 63 

Locomotives, rate of combustion in. .118, 120 

Luminous flames 114 

McFarlane, James, quoted 61 

McMurray, R. K., bridge wall 153 

Marriotte's law 30 



PAGE 

Marsilly, M., on coking 67 

Martin's furnace door 148 — 151 

Mayer, Dr 204 

Mechanical firing 218 

Mechanical intermixture and chemical 

combination 99 

Mechanical theory of heat 195, 203, 204 

Meunier-Dollfus 165 

Multiple proportions 101 

Muriate of zinc 99 

Molecules 3 

Molecules and atoms 5 

Molecules, motion of 3 

Molecules, number of atoms in 6 

Molecules, weights of 6 

Mott, Henry A., Jr., table of products 

obtained from coal 94 

Mount Vernon, N. Y., gas wks...263, 265, 270 

Neilson, heated air in furnaces 128 

Net combustible 117 

Newport puddling furnace 130 

Nitrogen 158 

Nitrogen and hydrogen 91 

Nitrogen and oxygen 29 

Nitrogen, molecular weight of 6 

Nitrogen, properties of 27 

Non-caking coals 61, 64 

Norwood, Dr., analysis by 55 

Orsat, M. De H 174 

Ougree iron works 162, 164 

Owen, D. D., analysis by... 74 

Oxygen 29 

Oxygen to be deducted from fuel 1S1 

Oxygen, molecular weight of 6 

Ozone 34 

Parrot coal 74 

Peat 35 

Peat, analysis of 40 

Peat charcoal , 42 

Peat formation 39 

Peat, product of distillation 41 

Peat, properties of 39 

Peat, use of in locomotives 41 

Peat, water in 40 

Peclet, on heated air 130 

Percy's classification of fuel 35 

Perforated pipes in furnaces 152 

Perpetual motion 22 

Peter, Prof., analysis by 58, 75 

Petroleum 245 



INDEX. 



305 



PAGE 

Petroleum, calorific power of 246 

Phosphorous in coal 85 

Phosphorous, molecular weight of 6 

Plautsof the coal period 17 

Ponsaid furnace 129 

Ponsard furnace, description of 290 

Ponsard recuperator 134 

Potential energy 11, 104 

Powdered fuel, experiments 234 

Pressure of gases, cause of 4 

Pressure, influence of in coking G7 

Pressure of air : 4 

Prideaux, T. S 129 

Prideaux, furnace door 143 

Prideaux, on combustion 132 

Products obtained from coal 94 

Products of combustion 158, 284 

Proximate analysis 81, 83 

Puddling furnace 213 

Qualitative analysis 81 

Quantitative analysis 81 

Rain, cause of 30 

Rankine, on heated gasses 137 

Rate of combustion 117 

Red ash 170 

Regnault, M 19G 

Regnault, M., analysis of lignites 51 

Reverberatory furnaces 131 

Rogers, H. D., classification of coal 52 

Ronchamp coal, rate of combustion 118 

Samples for analysis 82 

Semi-anthracite coal 77 

Semi-bituminous coal 76, 77 

Sesquioxide of iron 170 

Sheurer, Kestner and Meunier-Dollfus... 184 

Ships and spontaneous combustion 223 

Sigillaria or seal tree 17 

Silica in ashes 169 

Seimens, Dr. William 211 

Seimens' crucible furnace 267 

Seimens' furnaces 129 

Seimens' gas 278 

Seimens' gas temperature of flame 27S 

Seimens' gas and water-gas 265 

Seimens' regenerators 134, 231 

Seimens' regenerative gas furnace 285 

Skeel, Theron 139 

Smith's furnace door 219 

Smoke 142, 15'; 

Smoke, burning 16*' 

Smoke, prevention 1G1 



PAGE 

Smoke, sulphurous acid in 162 

Soot '. 161 

Soot, analysis of 165 

Soot, in flame 159 

Source of energy 16 

Specific heat 199, 133 

Specific heat and atomic weights 196 

Specific heat of carbon 88 

Specific heat of gases 197, 201 

Spontaneous combustion 223 

Steam jet for draft 136 

Steel, loss of heat in melting 285 

Stein on flame 115 

Structure of flame Ill 

Sunlight, chemical effects of 20 

Sun, rays of a source of motion 19 

Sun, the source of energy 16 

Stevenson's apparatus for burning pow- 

♦ deredfuel 239 

Strong's gas as a fuel 276 

Strong's gas, composition of 274 

Strong's gas, cost of 277 

Strong's gas, economic value of 275 

Strong's gas, for illuminating 281 

Strong's gas, for metallurgy 281 

Strong's gas, process for generating 261 

Sulphate of iron 166 

Sulphur 92, 158 

Sulphur a cause of corrosion 162 

Sulphur, action of on iron 167 

Sulphur, chemical relations of 92 

Sulphur in coal, determining the 85 

Sulphur in gas coal 63 

Sulphur in water-gas 273 

Sulphur, molecular weight of 6 

Sulphurous acid 149 

Sulphurous acid in smoke 162, 165 

Sulphurous oxide 158 

Symbols, not merely abbreviations 9 

Symbols, why used 8 

Symbolic formulas, how made 9 

Symbolic notation 8 

Temperature, advantages of a high 130 

Temperature, at which light is emitted.. 110 

Temperature, effect of a uniform 24 

Temperature, influence in coking 66 

Temperature, of combustion, table of.... 123 

Temperature, of fire 120 

Thermal power of fuels 178 

Thermodynamics, first law of 203 

Thompson's calorimeter 188 

Transmutation of energy 13 



306 



INDEX. 



PAGE 

Tynclall, estimate of Mayer and Joule... 204 
Tyndall, theory of combustion 107 

Unit of heat 206 

Unit of work 11 

U. S. Govt, experiments, furnace door.. 151 
U. S. Govt, experiments, powdered fuel, 234 

Vapor in the atmosphere 32 

Vincent, Chas. W., quoted 223 

Violette, M., quoted 36, 38 

Volatile matter in coal 52 

Waste gases 216 

Waste gases, the utilizing of 234 

Water and spontaneous combustion 230 

Water gas 260 

Water-gas, analysis of 265 

Water-gas and Siemens' gas 265 

Water-gas, objections to ; 283 

Water-gas, obtained per ton of coal 263 

Water, quantity of hydrogen in 90 

Water, specific heat of 199 



PAGE 

Water, temperature of max. density 207 

Whepleyand Storer 234 

White ash 170 

Wibel on flame 115 

Williams, C. Wye., furnace door 143 

Wills, Dr. Thos., quoted 92 

Wise, Field and Aydon 248 

Wormley, T. G., analysis by 60 

Wood 35 

Wood, as a fuel 36 

Wood, composition of 37 

Wood, conversion into coal 16, 22 

Wood, effect of exposure 16 

Wood, gas 282 

Wood, moisture in 36 

Woody fibre, formation of 20, 22 

Work converted into heat 13 

Wurtz, H., analysis by 245 

Youghiogheny coal 58, 62 

Zinc, action of muriatic acid on 99 



TABLES. 



PAGE 

I. Molecular weights 6 

II. Elements found in coal 7 

III. Compounds of nitrogen and oxygen .... 29 

IV. Water expelled from wood at various temperatures 36 

V. Composition of wood 37 

VI. Composition of charcoal 38 

VII. Composition of peat 40 

VIII. Products of the distillation of peat 41 

IX. Analysis and heating power of lignites 51 

X. Coals coked under different pressures 67 

XI. Composition of carbonic acid and oxide 88 

XII. Products obtained from coal 94 

XIII. Specific gravity, atomic weight and equivalent numbers of elements found 

in coal 103 

XIV. Rate of combustion, anthracite coal 119 

XV. Temperature of combustion 123 

XVI. Air required for combustion of various fuels 127 

XVII. Volume of gases at different temperatures 138 

XVIII. Experiments with the Ashcroft-Martin furnace door 151 

XIX. Heat developed by complete combustion 180 

XX. Units of heat in carbon 182 

XXI. Experimental and theoretical calorific power of coal 186 

XXII. Experimental calorific power of coal and lignite 187 

XXIII. Specific heat of simple gases 197 

XXIV. Products of specific heat into atomic weights 198 

XXV. Specific heat of fuels 200 

XXIV. Specific heatof gases 201 




.^^^^. 



Illl&ltl 



SECTION. 



a 



SHELF. 



2j 



NUMBER. 



